Research


Cell and Molecular Biology

Dr. KM Yao

Dr Yao, Kwok Ming (丘國明)

Associate Professor, Department of Biochemistry

BSc, MPhil (Hong Kong); PhD (Brandeis U, Mass.)

Contact
Email: kmyao@hku.hk
Tel: (852) 2819 9275; 2819 2812 (lab)
Office: L3-69, Laboratory Block, 21 Sassoon Road, Hong Kong

RGC-funded projects:

  • Investigating the functional involvement of PDZD2 in the regulation of pancreatic β cell gene expression and function
  • Activation of FoxM1 by the Raf/MEK/MAPK pathway and regulation at the G2/M phase Postgraduate Study of FoxM1 as effector of the DNA damage checkpoint Exploring the insulinotropic effect of secreted PDZD2

Postgraduate Research Projects Available:

  • Investigating the role of FOXM1 in the maintenance of human embryonic stem cell pluripotency and genome stability

Research Description:

My long-standing interest has been to understand how transcription factors regulate cell proliferation and differentiation. Our recent work centers around the Forkhead box transcription factor FoxM1 and the multi-PDZ protein PDZD2.

*FoxM1 and transcriptional regulation of cell cycle progression

Forkhead box (Fox) M1, previously known as WIN, HFH-11 and Trident, is a transcription factor ubiquitously expressed in proliferating cells. Its proliferation- instead of tissue-specific expression indicates a role in the regulation of cell division. FoxM1 levels display cell cycle phase-dependent changes; its expression is initiated just before entry into S phase and peaks at the G2/M phase of the cell cycle. Consistent with the predominant G2/M expression of FoxM1, loss-of-function analyses in FoxM1 -/- mouse embryonic fibroblasts (MEFs) and cancer cell lines by RNA interference have established a functional requirement of FoxM1 in mitosis. FoxM1-depleted cells had difficulty executing mitosis, and exhibited chromosomal instability and polyploidy. Further microarray and chromatin immunoprecipitation (ChIP) analyses revealed important G2/M-specific genes like Cyclin B1, Cdc25B, CENPA and Aurora B as direct targets of FoxM1. Considering the critical M phase function of FoxM1, it is not surprising that depletion of FoxM1 expression in various mouse models perturbed the development of multiple tissues and suppressed tumor formation.

My lab established inducible HeLa lines to first demonstrate the G2/M promoting effect of FoxM1c and its activation of the Cyclin B1 promoter. Using synchronized hTERT-BJ1 fibroblasts to examine the cell cycle phase-dependent regulation of FoxM1 function, my lab further demonstrated that FoxM1c, as the major isoform expressed in mitotic cells, is functionally activated by Raf/MEK/MAPK signaling at G2/M. Most recently, to address the functional effect of MAPK phosphorylation of FoxM1c (funded by CERG 7650/05M), we have established NIH3T3 lines with inducible over-expression of FoxM1c. Interestingly, inducible overexpression of FoxM1c slowed down instead of promoting cell cycle progression. These recent findings suggest that FoxM1c, when overexpressed in G1 and S phases to levels comparable to those in G2/M, exerts a S-phase delay effect and FoxM1 may be an effector of the DNA damage response.

FOXM1 and signal transduction pathway

* PDZD2 and regulation of pancreatic β-cell function and gene expression

Another major research focus is to understand the functional role of the multi-PDZ protein PDZD2. We first isolated PDZD2 in a screen for proteins interacting with E12, a bHLH transcription factor that binds to E-boxes within the insulin gene promoter.

PDZD2 (also named PIN-1, PAPIN, AIPC and most recently PDZK3) contains six PDZ-like domains. We demonstrated that PDZD2, which shows extensive homology to pro-IL-16, is localized mainly in the endoplasmic reticulum (ER). Pro-IL-16 is cleaved via a caspase 3-dependent mechanism to generate the secreted cytokine IL-16. Abundant expression of PDZD2 in the ER and its sequence similarity to pro-IL-16 suggest similar post-translational processing of PDZD2. Indeed, Western blot and mass spectrometry analysis of conditioned medium from cells transfected with epitope-tagged PDZD2 reveals secretion of a ~37 kDa PDZD2 protein (sPDZD2 for secreted PDZD2) that contains two PDZ domains. sPDZD2 expression was detected in multiple tissues. Further, sPDZD2 secretion is suppressed by mutation of a caspase-like recognition sequence or treatment with a caspase inhibitor. In summary, PDZD2 represents the first reported multi-PDZ protein processed by proteolytic cleavage to generate a secreted protein containing two PDZ domains.

Using an antiserum that recognizes both the full-length and secreted forms of PDZD2, we recently investigated the cellular distribution of PDZD2 in adult pancreas. Immunohistochemical analysis reveals a strong expression of PDZD2 in pancreatic islet β cells but not α cells. Consistent with the β cell-enriched expression of PDZD2, immunoblot analysis indicates expression of both full-length PDZD2 and sPDZD2 in the insulinoma cell line INS-1E. To test the effect of sPDZD2 on INS-1E cell proliferation, a recombinant sPDZD2 protein was synthesized. In culture media with limiting serum, co-incubation with sPDZD2 stimulates the proliferation of INS-1E cells. The mitogenic effect of sPDZD2 is concentration-dependent, and is associated with a slight inhibition of the insulin promoter activity at high sPDZD2 concentrations. As a mitogen of β-like cells, sPDZD2 will be useful for the optimization of β cell growth and differentiation in vitro.

PDZD2 immunostaining
PDZD2 western blot

Publications, Achievements, and Grants:

Recent Publications (*Corresponding author):

  • Li, C., Liu, V. W., Chan, D. W., Yao, K.-M., and H. Y. Ngan*. 2011. LY294002 and metformin cooperatively enhance the inhibition of growth and the induction of apoptosis of ovarian cancer cells. Int. J. Gynecol. Cancer 22: 15-22.
  • Yang, S., Yalamanchili, H. K., Li, X., Yao, K.-M., Sham, P. C., Zhang, M. Q., and J. Wang*. 2011. Correlated evolution of transcription factors and their binding sites. Bioinformatics 27: 2972-2978.
  • Lok, G. T., Chan, D. W., Liu, V. W., Hui, W. W., Leung, T. H., Yao, K.-M., and H. Y. Ngan*. 2011. Aberrant activation of ERK/FOXM1 signaling cascade triggers the cell migration/invasion in ovarian cancer cells. PLoS One 6(8):e23790.
  • Chan, D. W., Liu, V. W., Leung, L. Y., Yao, K.-M., Chan, K. K., Cheung, A. N., and H. Y. Ngan*. 2011. Zic2 synergistically enhances Hedgehog signalling through nuclear retention of Gli1 in cervical cancer cells. J. Pathol. 225: 525-534.
  • Cui, J., Wang, Z., Cheng, Q., Lin, R., Zhang, X. M., Leung, P. S., Copeland, N. G., Jenkins, N. A., Yao, K.-M.*, and J. D. Huang*. 2011. Targeted inactivation of kinesin-1 in pancreatic β-cells in vivo leads to insulin secretory deficiency. Diabetes 60: 320-330.
  • Shiu, S. Y.*, Pang, B., Tam, C. W., and K.-M., Yao. 2010. Signal transduction of receptor-mediated antiproliferative action of melatonin on human prostate epithelial cells involves dual activation of Gα(s) and Gα(q) proteins. J. Pineal Res. 49: 301-311.
  • Ma, R. Y., Tong, T. H., Leung, W. Y., and K.-M. Yao*. 2010. Raf/MEK/MAPK signaling stimulates the nuclear translocation and transactivating activity of FOXM1. Methods Mol. Biol. 647: 113-123.
  • Tsang, S. W., Shao, D., Cheah, K. S. E., Okuse, K., Leung, P. S., and K.-M. Yao*. 2010. Increased basal insulin secretion in Pdzd2-deficient mice. Mol. Cell Endocrinol. 315: 263-270.

Other Representative Publications

  • Thomas, M. K.*, Tsang, S. W., Yeung, M.-L., Leung, P. S., and K.-M. Yao*. 2009. The roles of the PDZ-containing proteins Bridge-1 and PDZD2 in the regulation of insulin production and pancreatic beta-cell mass. Curr. Protein Pept. Sci. 10: 30-36.
  • Leung, K. K., Suen, P. M., Lau, T. K., Ko, W. H., Yao, K.-M., P. S. Leung*. 2008. PDZ-domain containing-2 (PDZD2) drives the maturity of human fetal pancreatic progenitor-derived islet-like cell clusters with functional responsiveness against membrane depolarization. Stem Cells Dev. 18: 979-990.
  • Li, S. K., Smith, D. K., Leung, W. Y., Cheung, A. M., Lam, E. W., Dimri, G. P., and K.-M. Yao*. 2008. FoxM1c counteracts oxidative stress-induced senescence and stimulates Bmi-1 expression. J. Biol. Chem. 283: 16545-16553.
  • Tam, C. W., Cheng, A.S., Ma, R. Y. M., Yao, K.-M.*+, and S.Y.W. Shiu*+. 2006. Inhibition of prostate cancer cell growth by sPDZD2 protein, a potential autocrine prostate tumor suppressor.  Endocrinology. 147: 5023-5033. +Equal contribution 
  • Madureira, P.A., Varshochi, R., Constantinidou, D., Francis, R.E., Coombes, R.C., Yao, K.-M., and E.W. Lam*. 2006. The Forkhead box M1 protein regulates the transcription of the estrogen receptor alpha in breast cancer cells. J. Biol. Chem. 281:25167-25176.
  • Ma, R. Y. M., Tong, T. H. K., Cheung, A. M. S., Tsang, A. C. C., Leung, W. Y., and K.-M., Yao*. 2005. Raf/MEK/MAPK signaling stimulates the nuclear translocation and transactivating activity of FOXM1c. J. Cell Sci. 118: 795-806.
  • Yeung, M.-L., Tam, T. S. M., Tsang, A. C. C., and K.-M. Yao*. 2003. Proteolytic cleavage of PDZD2 generates a secreted peptide containing two PDZ domains.  EMBO Rep. 4: 412-418.
  • Yao, K.-M.*, M. Sha, Z. Lu, and G. Wong. 1997. Molecular analysis of a novel winged helix protein, WIN (renamed FOXM1): Expression pattern, DNA binding property and alternative splicing within the DNA binding domain.  J. Biol. Chem. 272: 19827-19836.