Zhaohua Irene Tang

Professor of Biology

Email: ztang@kecksci.claremont.edu
Office: Keck Science Center 201
Phone: 909-607-9067

Educational Background

Postdoctoral Fellow, California Institute of Technology, Pasadena, CA
Ph.D., University of California, Los Angeles
B.S., State University of New York at Stony Brook
Peking University Medical School, Beijing, P.R. of China

Courses Taught

• Regulation of the Cell-division Cycle (lecture)
• Physical Chemistry for Molecular Biology Program (lecture)
• Introductory Biology, lecture and lab (Molecular, Cell Biology and Genetics)
• Cell Biology, lecture and lab
• Cell Cycle, Diseases, and Aging (lecture)
• Biology 177 Biochemistry (Lecture)
• AISS (Accelerated Interdisciplinary Science Series)
• Bio 43 Introductory Biology Lecture and Lab

Research Interests

To investigate the functions of several protein kinases in the regulation of cell cycle progression and cell death, in the response to environmental factors, as well as in the cellular sensitivity to anticancer drugs, using a single-cell eukaryotic organism, fission yeast Schizosaccharomyces pombe as an in vivo model.
External Research Fund obtained:
NSF grant for Research in Undergraduate Institution (RUI)
NIH R15 Grant

Thesis Topics

• Cell signaling for the interplay between cell-division cycle and gene expression events such as pre-mRNA processing, mRNA export, as well as heterochromatic silencing in eukaryotes involving several protein kinases including Dsk1 and Kic1.
• Genomic studies on genes involved in the cellular sensitivity and resistance to platinum-based anticancer drugs.
• Genomic studies on conserved response networks to phenol derivatives as environmental stress factors.

Selected Publications

1. Mei Wu, Gang Feng, Buyu Zhang, Kaikun Xu, Zhen Wang, Sen Cheng, Cheng Chang, Aditi Vyas, Zhaohua Tang, and Xiaoyun Liu. (2020). Phosphoproteomics Reveals Novel Targets and Phosphoprotein Networks in Cell Cycle Mediated by Dsk1 Kinase. Journal of Proteome Research, accepted February 16, 2020   Accepted by Journal of Proteome Research/ACS Publications, 16 Feb 2020.
   Abstract – As the ortholog of human SR protein kinase 1 in fission yeast Schizosaccharomyces pombe, Dsk1 specifically phosphorylates SR proteins (serine/arginine-rich proteins) and promotes splicing of nonconsensus introns. The SRPK (SR protein-specific kinase) family performs highly conserved functions in eukaryotic cells including cell proliferation, differentiation, development, and apoptosis. Although Dsk1 was originally identified as a mitotic regulator, its specific targets involved in cell cycle have yet been unexplored. In this study, using a phosphoproteomics approach, we examined differential protein phosphorylation between wild-type cells and dsk1-deletion mutants. We found reduced phosphorylation of 149 peptides corresponding to 133 proteins in the dsk1-null cells. These proteins are involved in various cellular processes, including cytoskeleton organization and signal transduction, and specifically enriched in multiple steps of cell cycle control. Further, targeted MS analyses and in vitro biochemical assays established Cdr2 protein kinase and kinesin motor Klp9 as novel substrates of Dsk1, which function in cell size control for mitotic entry and in chromosome segregation for mitotic exit, respectively. The phosphoprotein networks mediated by Dsk1 reveal, for the first time, the molecular links connecting Dsk1 to mitotic phase transition, sister-chromatid segregation, and cytokinesis, providing further evidence of Dsk1’s diverse influence on cell cycle progression and regulation.
   Article
2. 20 student authors (Alhoch et al.), 6 faculty authors ( K. Purvis-Roberts, C. Selassie, G. Edwalds-Gilbert, M. C. Negritto, R. Wang and Z. Tang). (2019). Comparative Genomic Screen in Two Yeasts Reveals Conserved Pathways in the Response Network to Phenol Stress. G3 Genes Genomes Genetics  American Society of Genetics 9: 639-650.
   Abstract – Living organisms encounter various perturbations, and response mechanisms to such perturbations are vital for species survival. Defective stress responses are implicated in many human diseases including cancer and neurodegenerative disorders. Phenol derivatives, naturally occurring and synthetic, display beneficial as well as detrimental effects. The phenol derivatives in this study, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and bisphenol A (BPA), are widely used as food preservatives and industrial chemicals. Conflicting results have been reported regarding their biological activity and correlation with disease development; understanding the molecular basis of phenol action is a key step for addressing issues relevant to human health. This work presents the first comparative genomic analysis of the genetic networks for phenol stress response in an evolutionary context of two divergent yeasts, Schizosaccharomyces pombe and Saccharomyces cerevisiae. Genomic screening of deletion strain libraries of the two yeasts identified genes required for cellular response to phenol stress, which are enriched in human orthologs. Functional analysis of these genes uncovered the major signaling pathways involved. The results provide a global view of the biological events constituting the defense process, including cell cycle arrest, DNA repair, phenol detoxification by V-ATPases, reactive oxygen species alleviation, and endoplasmic reticulum stress relief through ergosterol and the unfolded protein response, revealing novel roles for these cellular pathways.
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3. Zhaohua Tang and Gretchen Edwalds-Gilbert. (2016). Nucleic Acid and Protein Sample Preparation from Yeasts (Chapter 20). Peer-reviewed Book, Sample Preparation Techniques for Soil, Plant, and Animal Samples, Springer Protocols Handbooks M. Micic (ed.), Springer, New York DOI 10.1007/978-1-4939-3185-9_20 © Springer.
4. Zhaohua Tang. (2015). Model Organisms for Studying the Cell Cycle (Chapter 2). Peer-reviewed Book, Cell Cycle Oscillators: Methods and Protocols, Methods in Molecular Biology Amanda S. Coutts and Louise Weston (eds.), Springer, New York 1342: 21-57.
5. Zhaohua Tang, Maria Luca, Laura Taggart-Murphy, Jessica Portillio, Cathey Chang, Ayse Guven, Ren-Jang Lin, Johanne Murray, and Antony Carr. (2012). Interacting Factors and Cellular Localization of SR Protein-specific Kinase Dsk1. Experimental Cell Research 318 (16): 2071-2084.
   Abstract – Schizosaccharomyces pombe Dsk1 is an SR protein-specific kinase (SRPK), whose homologues have been identified in every eukaryotic organism examined. Although discovered as a mitotic regulator with protein kinase activity toward SR splicing factors, it remains largely unknown about what and how Dsk1 contributes to cell cycle and pre-mRNA splicing. In this study, we investigated the Dsk1 function by determining interacting factors and cellular localization of the kinase. Consistent with its reported functions, we found that pre-mRNA processing and cell cycle factors are prominent among the proteins co-purified with Dsk1. The identification of these factors led us to find Rsd1 as a novel Dsk1 substrate, as well as the involvement of Dsk1 in cellular distribution of poly(A)+ RNA. In agreement with its role in nuclear events, we also found that Dsk1 is mainly localized in the nucleus during G2 phase and at mitosis. Furthermore, we revealed the oscillation of Dsk1 protein in a cell cycle-dependent manner. This paper marks the first comprehensive analysis of in vivo Dsk1-associated proteins in fission yeast. Our results reflect the conserved role of SRPK family in eukaryotic organisms, and provide information about how Dsk1 functions in pre-mRNA processing and cell-division cycle.
   Article – https://www.sciencedirect.com/science/article/abs/pii/S0014482712002686?via%3Dihub
6. Zhaohua Tang, Maria Luca, Jessica Portillio, Benson Ngo, Cathey Chang, Teresa Wen, Johanne Murray, and Antony Carr. (2011). LAMMER Kinase Kic1 Is Involved in Pre-mRNA Processing. Experimental Cell Research  317: 2308-2320.
   Abstract – The LAMMER kinases are conserved through evolution. They play vital roles in cell growth/differentiation, development, and metabolism. One of the best known functions of the kinases in animal cells is the regulation of pre-mRNA splicing. Kic1 is the LAMMER kinase in fission yeast Schizosaccharomyces pombe. Despite the reported pleiotropic effects of kic1+ deletion/overexpression on various cellular processes the involvement of Kic1 in splicing remains elusive. In this study, we demonstrate for the first time that Kic1 not only is required for efficient splicing but also affects mRNA export, providing evidence for the conserved roles of LAMMER kinases in the unicellular context of fission yeast. Consistent with the hypothesis of its direct participation in multiple steps of pre-mRNA processing, Kic1 is predominantly present in the nucleus during interphase. In addition, the kinase activity of Kic1 plays a role in modulating its own cellular partitioning. Interestingly, Kic1 expression oscillates in a cell cycle-dependent manner and the peak level coincides with mitosis and cytokinesis, revealing a potential mechanism for controlling the kinase activity during the cell cycle. The novel information about the in vivo functions and regulation of Kic1 offers insights into the conserved biological roles fundamental to LAMMER kinases in eukaryotes.
   [Article – URL not found]
7. Zhaohua Tang. (2010). The Domino and Clock Models of Cell Cycle Regulation. Nature Education 3(9): 56.
   Article
8. Nicole M. Duggan* and Zhaohua Tang. (2010). The Formation of Heterochromatin and RNA interference. Nature Education 3(9): 5.
   [Article – not found]
9. Tang, Z., Alaei, Tsurumi, A., C., Wilson, C., S., Chiu, C., Oya, J., and Ngo, B. (2007). Dsk1 Kinase Phosphorylates SR Proteins and Regulates Their Cellular Localization in Fission Yeast. Biochemical Journal 405 (1): 21-30.
   Abstract – Evolutionarily conserved SR (serine-arginine rich) proteins are important factors for alternative splicing and their activity is modulated by SR protein-specific kinases (SRPKs). We previously identified Dsk1p as the orthologue of human SRPK1 in fission yeast. In addition to its similarity of gene structure to higher eukaryotes, fission yeast Schizosaccharomyces pombe is a unicellular eukaryotic organism in which alternative splicing takes place. In this study, we have revealed for the first time that SR proteins, Srp1p and Srp2p, are the in vivo substrates of Dsk1p in S. pombe. Moreover, the cellular localization of the SR proteins and Prp2p splicing factor is dependent on dsk1+: Dsk1p is required for the efficient nuclear localization of Srp2p and Prp2p, while it promotes the cytoplasmic distribution of Srp1p, thereby differentially influencing the destinations of these proteins in the cell. This work offers the first biochemical and genetic evidence for the in vivo targets of the SRPK1 orthologue, Dsk1p, in S. pombe and the significant correlation between Dsk1p-mediated phosphorylation and the cellular localization of the SR proteins, providing information about the physiological functions of Dsk1p. Furthermore, the results demonstrate that the regulatory function of SRPKs in the nuclear targeting of SR proteins is conserved from fission yeast to human, indicating a general mechanism of reversible phosphorylation to control the activities of SR proteins in RNA metabolism through cellular partitioning.
   [Article – URL not found]
10. Huang, C-J, Tang, Z, Lin, R.-J, and Tucker, P.W. (2007). Phosphorylation by SR kinases regulates the binding of PTB-associated splicing factor (PSF) to the pre-mRNA polypyrimidine tract. FEBS lett 581(2): 223-232.
    Abstract- PSF (PTB-associated splicing factor) is a multi-functional protein that participates in transcription and RNA processing. While phosphorylation of PSF has been shown to be important for some functions, the sites and the kinases involved are not well understood. Although PSF does not contain a typical RS domain, we report here that PSF is phosphorylated in vivo to generate an epitope(s) that can be recognized by a monoclonal antibody specific for phosphorylated RS motifs within SR proteins. PSF can be phosphorylated by human and yeast SR kinases in vivo and in vitro at an isolated RS motif within its N terminus. A functional consequence of SR phosphorylation of PSF is to inhibit its binding to the 3′ polypyrimidine tract of pre-mRNA. These results indicate that PSF is a substrate of SR kinases whose phosphorylation regulates its RNA binding capacity and ultimate biological function.
11. Tang, Z., Mandel, L., Yean, S.-L., Lin*, C.X., Chen*, T., Yanagida, M., and Lin, R.-J. (2003). The Kic1 Kinase of Schizosaccharomyces pombe Is a CLK/STY Orthologue That Regulates Cell-Cell Separation. Experimental Cell Research 283: 101-115.
    Abstract – The CLK/STY kinases are a family of dual-specificity protein kinases implicated in the regulation of cellular growth and differentiation. Some of the kinases in the family are shown to phosphorylate serine–arginine-rich splicing factors and to regulate pre-mRNA splicing. However, the actual cellular mechanism that regulates cell growth, differentiation, and development by CLK/STY remains unclear. Here we show that a functionally conserved CLK/STY kinase exists in Schizosaccharomyces pombe, and this orthologue, called Kic1, regulates the cell surface and septum formation as well as a late step in cytokinesis. The Kic1 protein is modified in vivo, likely by phosphorylation, suggesting that it can be involved in a control cascade. In addition, kic1+ together with dsk1+, which encodes a related SR-specific protein kinase, constitutes a critical in vivo function for cell growth. The results provide the first in vivo evidence for the functional conservation of the CLK/STY family through evolution from fission yeast to mammals. Furthermore, since cell division and cell–cell interaction are fundamental for the differentiation and development of an organism, the novel cellular role of kic1+ revealed from this study offers a clue to the understanding of its counterparts in higher eukaryotes.
    [Article – URL not found]
12.  Portal, D., Lobe, G.S., Kadener, S., Prasad, J., Espinosa, J.M., Pereira, C.A., Tang, Z., Lin, R.-J., Manley, J.L., Kornblihtt, A.R., Flawia M.M., and Torres H.N. (2003). Trypanosoma cruzi TcSRPK, The First Protozoan Member of The SRPK Family, Is Biochemically and Functionally Conserved with Metazoan SR Protein-specific Kinases. Molecular and Biochemical Parasitology 127: 9-21.
    Abstract – A novel SR protein-specific kinase (SRPK) from the SRPK family was identified for the first time in a protozoan organism. The primary structure of the protein, named TcSRPK, presents a significant degree of identity with other metazoan members of the family. In vitro phosphorylation experiments showed that TcSRPK has the same substrate specificity relative to other SRPKs. TcSRPK was able to generate a mAb104-recognized phosphoepitope, a SRPK landmark. Expression of TcSRPK in different Schizosaccharomyces pombe strains lead to conserved phenotypes, indicating that TcSRPK is a functional homologue of metazoan SRPKs. In functional alternative splicing assays in vivo in HeLa cells, TcSRPK enhanced SR protein-dependent inclusion of the EDI exon of the fibronectin minigene. When tested in vitro, it inhibited splicing either on nuclear extracts or on splicing-deficient S100 extracts complemented with ASF/SF2. This inhibition was similar to that observed with human SRPK1. This work constitutes the first report of a member of this family of proteins and the existence of an SR-network in a protozoan organism. The implications in the origins and control of splicing are discussed.
    [Article – URL not found]
13. Portal, D., Espinosa J.M., Lobo G.S., Kadener S., Pereira C.A., De La Mata M., Tang Z., Lin R.-J., Kornblihtt A.R., Baralle F.E., Flawia M.M., and Torres H.N. (2003). An Early Ancestor in The Evolution of Splicing: A Trypanosoma Cruzi Serine-arginine-rich Protein (TcSR) Is Functional in Cis-splicing. Molecular and Biochemical Parasitology 127: 37-46.
    Abstract – A novel serine–arginine-rich protein designated TcSR was identified in Trypanosoma cruzi. The deduced amino acid sequence reveals that TcSR is a member of the SR protein family of splicing factors that contains two RNA-binding domains at the N-terminal side and several serine–arginine repeats at the COOH-terminus. Over expression of either TcSR or the human SR-protein associated splicing factor/splicing factor 2 (ASF/SF2) in wild-type Schizosaccharomyces pombe, provoked an elongated phenotype similar to that of fission yeast over expressing the SR-containing splicing factor Prp2, a U2AF65 orthologue. When a double mutant strain lacking two SR protein-specific protein kinases was used, expression of TcSR or human SR ASF/SF2 splicing factor reverted the mutant to a wild-type phenotype. Transient expression of TcSR in HeLa cells stimulated the inclusion of the EDI exon of human fibronectin in an in vivo functional alternative cis-splicing assay. Inclusion was dependent on a splicing enhancer sequence present in the EDI exon. In addition, TcSR and peptides carrying TcSR-RS domain sequences were phosphorylated by a human SR protein kinase. These results indicate that TcSR is a member of the SR splicing network and that some components common to the trans- and cis-splicing machineries evolved from the early origins of the eukaryotic lineage.
    [Article – URL not found]
14. Tang, Z., Käufer, N. F., and Lin, R.-J. (2002). Interactions Between Two Fission Yeast SR-Related Proteins and Their Modulation by Phosphorylation. Biochemical Journal   368: 527-534.
    Abstract – The unexpected low number of genes in the human genome has triggered increasing attention to alternative pre-mRNA splicing, and serine/arginine-rich (SR) proteins have been correlated with the complex alternative splicing that is a characteristic of metazoans. SR proteins interact with RNA and splicing protein factors, and they also undergo reversible phosphorylation, thereby regulating constitutive and alternative splicing in mammals and Drosophila. However, it is not clear whether the features of SR proteins and alternative splicing are present in simple and genetically tractable organisms, such as yeasts. In the present study, we show that the SR-like proteins Srp1 and Srp2, found in the fission yeast Schizosaccharomyces pombe, interact with each other and the interaction is modulated by protein phosphorylation. By using Srp1 as bait in a yeast two-hybrid analysis, we specifically isolated Srp2 from a random screen. This Srp interaction was confirmed by a glutathione-S-transferase pull-down assay. We also found that the Srp1�Srp2 complex was phosphorylated at a reduced efficiency by a fission yeast SR-specific kinase, Dis1-suppression kinase (Dsk1). Conversely, Dsk1-mediated phosphorylation inhibited the formation of the Srp complex. These findings offer the first example in fission yeast for interactions between SR-related proteins and the modulation of the interactions by specific protein phosphorylation, suggesting that a mammalian-like SR protein function may exist in fission yeast.
15. Tang, Z., Kuo*, T., Shen*, J., and Lin, R.-J. (2000). Biochemical and Genetic Conservation of Fission Yeast Dsk1 and Human SRPK1. Mol. Cell. Biol 20(3): 816-824.
    Abstract – Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protein kinases constitute control circuits to regulate pre-mRNA splicing and coordinate splicing with transcription in mammalian cells. We present here the finding that similar SR networks exist in Schizosaccharomyces pombe. We previously showed that Dsk1 protein, originally described as a mitotic regulator, displays high activity in phosphorylating S. pombe Prp2 protein (spU2AF59), a homologue of human U2AF65. We now demonstrate that Dsk1 also phosphorylates two recently identified fission yeast proteins with RS repeats, Srp1 and Srp2, in vitro. The phosphorylated proteins bear the same phosphoepitope found in mammalian SR proteins. Consistent with its substrate specificity, Dsk1 forms kinase-competent complexes with those proteins. Furthermore, dsk1+ gene determines the phenotype of prp2+ overexpression, providing in vivo evidence that Prp2 is a target for Dsk1. The dsk1-null mutant strain became severely sick with the additional deletion of a related kinase gene. Significantly, human SR protein-specific kinase 1 (SRPK1) complements the growth defect of the double-deletion mutant. In conjunction with the resemblance of dsk1+ and SRPK1 in sequence homology, biochemical properties, and overexpression phenotypes, the complementation result indicates that SRPK1 is a functional homologue of Dsk1. Collectively, our studies illustrate the conserved SR networks in S. pombe consisting of RS domain-containing proteins and SR protein-specific kinases and thus establish the importance of the networks in eucaryotic organisms.
    Article
16. Tang, Z., Yanagida, M., and Lin, R.-J. (1998). Fission Yeast Mitotic Regulator Dsk1 Is an SR Protein-Specific Kinase. J. Biol. Chem   273: 5963-5969.
    Abstract – From the Department of Molecular Biology, Beckman Research Institute of the City of Hope, Duarte, California 91010 and the Department of Biophysics, Faculty of Science, Kyoto University, Kyoto 606, Japan Intricate interplay may exist between pre-mRNA splicing and the cell division cycle, and fission yeast Dsk1 appears to play a role in such a connection. Previous genetic analyses have implicated Dsk1 in the regulation of chromosome segregation at the metaphase/anaphase transition. Yet, its protein sequence suggests that Dsk1 may function as a kinase specific for SR proteins, a family of pre-mRNA splicing factors containing arginine-serine repeats. Using an in vitro system with purified components, we showed that Dsk1 phosphorylated human and yeast SR proteins with high specificity. The Dsk1-phosphorylated SF2/ASF protein was recognized strongly by a monoclonal antibody (mAb104) known to bind the in vivo phosphoepitope shared by SR proteins, indicating that the phosphorylation sites resided in the RS domain. Moreover, the fission yeast U2AF65 homolog, Prp2/Mis11 protein, was phosphorylated more efficiently by Dsk1 than by a human SR protein-specific kinase, SRPK1. Thus, these in vitro results suggest that Dsk1 is a fission yeast SR protein-specific kinase, and Prp2/Mis11 is likely an in vivo target for Dsk1. Together with previous genetic data, the studies support the notion that Dsk1 may play a role in coordinating pre-mRNA splicing and the cell division cycle.
    [Article – URL not found]
17. Coleman, T.R., Tang, Z., and Dunphy, W.G. (1993). Negative Regulation of the Weel Protein Kinase by Direct Action of the Nim1/Cdr1 Mitotic Inducer. Cell 72: 919-929.
18. Tang, Z., Coleman, T.R., and Dunphy, W.G. (1993). Two Distinct Mechanisms for Negative Regulation of the Wee1 Protein Kinase. EMBO   12(9): 3427-3436.
    Abstract – The Wee1 protein kinase negatively regulates the entry into mitosis by catalyzing the inhibitory tyrosine phosphorylation of the Cdc2 protein. To examine the potential mechanisms for Wee1 regulation during the cell cycle, we have introduced a recombinant form of the fission yeast Wee1 protein kinase into Xenopus egg extracts. We find that the Wee1 protein undergoes dramatic changes in its phosphorylation state and kinase activity during the cell cycle. The Wee1 protein oscillates between an underphosphorylated 107 kDa form during interphase and a hyperphosphorylated 170 kDa version at mitosis. The mitosis-specific hyperphosphorylation of the Wee1 protein results in a substantial reduction in its activity as a Cdc2-specific tyrosine kinase. This phosphorylation occurs in the N-terminal region of the protein that lies outside the C-terminal catalytic domain, which was recently shown to be a substrate for the fission yeast Nim1 protein kinase. These experiments demonstrate the existence of a Wee1 regulatory system, consisting of both a Wee1-inhibitory kinase and a Wee1-stimulatory phosphatase, which controls the phosphorylation of the N-terminal region of the Wee1 protein. Moreover, these findings indicate that there are apparently two potential mechanisms for negative regulation of the Wee1 protein, one involving phosphorylation of its C-terminal domain by the Nim1 protein and the other involving phosphorylation of its N-terminal region by a different kinase.