PhD Biochemistry, Hyderabad, India , 1986
Immunology and Cell Biology of Melanoma, 1992
Memorial Sloan-Kettering Cancer Center, New York
My laboratory is interested in understanding molecular mechanisms of skin cancer melanoma tumorigenesis and progression, and basic cell and molecular biology of epidermal melanocytes. The specific areas of research are:
BRAF oncogene-induced autophagy as melanoma tumor suppressor mechanism
Activating mutations in NRAS and BRAF are found frequently in cutaneous melanomas. Because concurrent mutations of both BRAF and RAS are extremely rare, it is thought that transformation by RAS and BRAF occurs through a common mechanism. Also, there is evidence for a relationship of synthetic lethality between NRAS and BRAF oncogenes that leads to selection against cells with a hyperactive mitogen-activated protein kinase (MAPK) pathway. However, it is not known whether the hyperactivation of the MAPK pathway by overexpression of either oncogene alone could also inhibit melanoma tumorigenesis. Research in my laboratory showed that in melanoma cells with oncogenic BRAF (mBRAF), high levels of mBRAF induce hyperactivation of ERK and senescence-like phenotype and trigger autophagy by inhibiting the mammalian target of rapamycin complex (mTORC) signaling. Growth inhibition and cell death caused by high mBRAF levels can be partially rescued by downregulation of BRAF protein or inhibition of autophagy, but not by inhibition of the MAPK or apoptotic pathways. Quantitative immunohistochemical analysis (AQUA) of human melanomas and cell lines showed a significant positive correlation between the levels of BRAF protein and autophagy marker light chain 3 (LC3). We are currently investigating mechanisms of autophagy induction by BRAF oncogene.
Melanoma transdifferentiation and tumor progression: crosstalk between BRAF and Notch signaling
My laboratory has previously identified expression of neuronal marker MAP2 in melanoma. This marker is (a) activated in cutaneous primary melanoma and (b) inversely associated with melanoma tumor progression. We also showed that ectopic expression of MAP2 in metastatic melanoma cells inhibits cell growth by inducing mitotic spindle defects and apoptosis. However, molecular mechanisms of regulation of MAP2 gene expression in melanoma are not understood. Recently, we showed that in melanoma cells neuronal marker MAP2 expression is induced by the demethylating agent 5-aza-2'-cytidine, and MAP2 promoter is progressively methylated during melanoma progression, indicating that epigenetic mechanisms are involved in silencing of MAP2 in melanoma. Because MAP2 promoter activity levels in melanoma cell lines also correlated with activating mutation in BRAF, a gene that is highly expressed in neurons, we hypothesized that BRAF signaling is involved in MAP2 expression. We showed that hyperactivation of BRAF-MEK signaling activates MAP2 expression in melanoma cells by two independent mechanisms, promoter demethylation or down-regulation of neuronal transcription repressor HES1. We are investigating the role of HES1 target genes in melanoma transdifferentiation and melanoma tumor progression.
A working model of melanoma transdifferentiation and crosstalk between BRAF and Notch
Protein-protein interactions in melanosome biogenesis
By virtue of the presence of multiple protein-protein interaction and signaling domains, PDZ proteins play important roles in assembling protein complexes that participate in diverse cell biological processes. We showed earlier that PDZ protein GIPC is involved in melanosomal protein trafficking. GIPC is a versatile PDZ protein that binds a variety of target proteins in different cell types. In previous studies we showed that, in epidermal melanocytes, GIPC interacts with newly synthesized melanosomal protein TRP1 in the Golgi region and proposed that this interaction may facilitate intracellular trafficking of TRP1. However, since GIPC contains a single PDZ domain and no other known protein interaction motifs, it is not known how GIPC-TRP1 interaction affects melanosome biogenesis and/or melanin pigmentation. Recently, we showed that in human primary melanocytes GIPC interacts with AKT-binding protein APPL (adaptor protein containing pleckstrin homology, leucine zipper and phosphotyrosine binding domains), which readily co-precipitates with newly synthesized TRP1. Knockdown of either GIPC or APPL inhibits melanogenesis by decreasing tyrosinase protein levels and enzyme activity. In melanocytes, APPL exists in a complex with GIPC and phospho-AKT. Inhibition of AKT phosphorylation using a PI3-kinase inhibitor abolishes this interaction and results in retardation TRP1 in the Golgi. Ongoing research is aimed at understanding the dynamics of these interactions and their role in melanosome biogenesis.
Calcium homeostasis in melanocytes and role of transient receptor potential Melastatin 1 (TRPM1) glutamate receptor signaling skin pigmentation
Transient receptor potential melastatin (TRPM) is a subfamily of ion channels that are involved in sensing taste, ambient temperature, low pH, osmolarity, and chemical ligands. Melastatin 1/TRPM1, the founding member, was originally identified as melanoma metastasis suppressor based on its expression in normal pigment cells in the skin and the eye but not in aggressive, metastasis-competent melanomas. The role of TRPM1 and its regulation in normal melanocytes and in melanoma progression is not understood. Here, we studied the relationship of TRPM1 expression to growth and differentiation of human epidermal melanocytes. TRPM1 expression and intracellular Ca(2+) levels are significantly lower in rapidly proliferating melanocytes compared to the slow growing, differentiated melanocytes. Recently, we showed that lentiviral shRNA-mediated knockdown of TRPM1 results in reduced intracellular Ca(2+) and decreased Ca(2+) uptake suggesting a role for TRPM1 in Ca(2+) homeostasis in melanocytes. TRPM1 knockdown also resulted in a decrease in tyrosinase activity and intracellular melanin pigment. Expression of the tumor suppressor p53 by transfection or induction of endogenous p53 by ultraviolet B radiation caused repression of TRPM1 expression accompanied by decrease in mobilization of intracellular Ca(2+) and uptake of extracellular Ca(2+). Ongoing research is aimed at understanding the role of glutamate receptors in modulating TRPM1 activity and regulation of melanin pigmentation.
Kedlaya, R., Kandala, G., Liu, T. F., Maddodi, N., Devi. S., and Setaluri, V. (2011) Interactions between GIPC-APPL and GIPC-TRP1 regulate melanosomal protein trafficking and melanogenesis in human melanocytes Archives of Biochemistry and Biophysics, 508: 227-233.
Syed, D. N., Afaq, F., Maddodi, N., Johnson, J. J., Sarfaraz, S., Ahmad. A., Setaluri, V., and Mukhtar, H (2011) Inhibition of human melanoma cell growth by the dietary flavonoid fisetin is associated with disruption of Wnt/β-catenin signaling and decreased Mitf levels. Journal of Investigative Dermatology Epub. Feb 24
Goswami, S., Tarapore, R. S., Teslaa, J. J., Grinblat, Y., Setaluri, V., and Spiegelman, V. S. (2010) MicroRNA-340-mediated degradation of microphthalmia-associated transcription factor mRNA is inhibited by the coding region determinant-binding protein. Journal of Biological Chemistry, 285: 20532-20540.
Maddodi, N. and Setaluri, V. (2010) Prognostic significance of melanoma differentiation and transdifferentiation. Cancers 2: 989-999
Xu, X., Kedlaya, R., Ikeda, S., Justice, M. J., Setaluri, V., and Ikeda, A. (2010) Mutation in archain 1, a subunit of COPI coatomer complex, causes diluted coat color and Purkinje cell degeneration. PLoS Genetics 6: e1000956
Maddodi, N., Huang, W., Havighurst, T., Kim, K., Longley, J., and Setaluri, V. (2010) Hyperactivation of Oncogenic BRAF Triggers Autophagy and Inhibits Melanoma Tumor Growth in vitro and in vivo. Journal of Investigative Dermatology. 130:1657-1667.
Maddodi, N., Bhat, K. M. R., Devi, S., Zhang, S-C., and Setaluri, V. (2010) Oncogenic BRAFV600E Induces Expression of Neuronal Differentiation Marker MAP2 in Melanoma Cells by Promoter Demethylation and Downregulation of Transcriptional Repressor HES1. Journal of Biological Chemistry 285:242-54
Devi, S., Kedlaya, R., Maddodi, N., Bhat, K. M. R., Weber, C. S., Valdivia, H., and Setaluri, V. (2009) Calcium homeostasis in human melanocytes: Role of transient receptor potential melastatin 1 (TRPM1) and its regulation by Ultraviolet Light. American Journal of Physiology-Cell Physiology 297: C679-687.
Schmit, T. L., Zhong, W., Setaluri, V., Spiegelman, V. S, and Ahmad, N. (2009) Targeted depletion of Polo-like kinase (Plk) 1 through lentiviral shRNA or a small-molecule inhibitor causes mitotic catastrophe and induction of apoptosis in human melanoma cells. Journal of Investigative Dermatology 129:2843-2853.
Bin Hafeez, B., Adhami, V. M., Asim, M., Siddiqui, I. A., Bhat, K. M., Zhong, W., Saleem, M., Din, M., Setaluri, V., Mukhtar, H. (2009) Targeted knockdown of Notch1 inhibits invasion of human prostate cancer cells concomitant with inhibition of matrix metalloproteinase-9 and urokinase plasminogen activator. Clinical Cancer Research 15: 452-459.
Maddodi, N., Setaluri, V. (2008) Role of UV in Cutaneous Melanoma. Photochemistry and Photobiology 84:528-536