Molecular Mechanism of AGC Kinases in Human Malignant

The maintenance of normal cell function and tissue homeostasis is dependent on the precise regulation of multiple signaling pathways that control cellular decisions to either proliferate, differentiate, arrest cell growth, or initiate programmed cell death (apoptosis). Cancer arises when clones of mutated cells escape this balance and proliferate inappropriately without compensatory apoptosis. Deregulated cell growth occurs as a result of perturbed signal transduction that modulates or alters cellular behavior or function to keep the critical balance between the rate of cell-cycle progression (cell division) and cell growth (cell mass) on one hand, and programmed cell death (apoptosis, autophagy) on the other. AGC kinases are activated downstream of a wide range of extracellular stimuli by distinct mechanisms. AGC kinase members such as Aurora-A and Akt regulate fundamental cellular functions including cell cycle, cell growth and survival. Inappropriate activation of those kinases has been associated with the development of diseases such as diabetes, autoimmunity, and cancer. The molecular mechanism of AGC kinases including Aurora-A and Akt involved in human cancers indicates that Aurora-A and Akt are important targets for cancer therapeutic strategies. We demonstrate, for the first time, that Aurora-A interacts with AR and phosphorylates AR at Thr282 and Ser293 in vitro and in vivo. Aurora-A induces AR transactivation activity in a phosphorylation-dependent manner. Ectopic expression Aurora-A in LNCaP cells induces the PSA expression and cell survival whereas knockdown of Aurora-A sensitizes LNCaP-RF cells to apoptosis and cell growth arrest. These data indicate that AR is a substrate of Aurora-A and that elevated Aurora-A could contribute to androgen-independent cell growth by phosphorylation and activation of AR. The NACHT leucine-rich repeat protein 1 (NALP1) is a member of the Ced-4 family and locates at chromosome 17p13.2 near TP53 locus. Here we demonstrated frequent somatic mutations and epigenetic silence of the NALP1 in human non-small cell lung, breast, ovarian and colon cancer. Restoration of NALP1 resulted in the inhibition of tumorigenic activity of the cell lines with NALP1 alterations. In addition to apoptosis, the cells expressing NALP1 largely undergo autophagy. Expression of NALP1 induces PI3KC3 kinase activity through directly interacts with Beclin 1, a protein required for activation of PI3KC3. Moreover, Akt phosphorylates NALP1 and disrupts the interaction between NALP1 and Beclin 1, leading to abrogation of NALP1-induced PI3KC3 activation and autophagy. Taken collectively, these data indicate that the NALP1 is a novel tumor suppressor gene on chromosome 17p13 and plays an important role in tumorigenesis by regulation of Beclin 1/PI3KC3 autophagic pathway and that Akt inhibits autophagy through regulation of NALP1/Beclin/ PI3KC3 cascade