The FHIT gene is arguably the most commonly altered gene in cancer which is inactivated in about 60% of human tumors. Studies on transgenic mice carrying one or two inactivated Fhit alleles show increased rates of spontaneous and carcinogen-induced cancers. Furthermore, Fhit overexpression can enhance the susceptibility of many cancer cell types to exogenous inducers of apoptosis. G proteins are intricately involved in the control of cell growth and proliferation, therefore the association between Fhit and Gα subunits, as well as the signaling influence they have together on cellular regulations were determined. Earlier investigations by others have demonstrated that the association of Flag-Fhit with Gα_q and Gα₁₆ proteins occured in a Gα activation dependent manner. In order to identify...[ Read more ]

The FHIT gene is arguably the most commonly altered gene in cancer which is inactivated in about 60% of human tumors. Studies on transgenic mice carrying one or two inactivated Fhit alleles show increased rates of spontaneous and carcinogen-induced cancers. Furthermore, Fhit overexpression can enhance the susceptibility of many cancer cell types to exogenous inducers of apoptosis. G proteins are intricately involved in the control of cell growth and proliferation, therefore the association between Fhit and Gα subunits, as well as the signaling influence they have together on cellular regulations were determined. Earlier investigations by others have demonstrated that the association of Flag-Fhit with Gα_q and Gα₁₆ proteins occured in a Gα activation dependent manner. In order to identify the binding domain for the associating proteins, a chimeric approach was implemented to identify amino acid 295 to 374 on the C terminal of Gα₁₆ as the minimal site for Fhit association. The same region is known to be responsible for the coupling to the GPCR. Fhit associated preferably to activated Gα₁₆ protein, the result therefore suggests a possible cascade that upon GPCR activation, it activates Gα₁₆ protein, Fhit may then compete with GPCR for the receptor coupling site on activated Gα₁₆ protein, and hinders the thereafter downstream signaling for cell proliferation. Gα₁₆ induces ERK phosphorylation through activating Ras, and therefore the MAPK pathway. Upon association, Fhit did not seem to affect the ability of Gα₁₆ to induce ERK phosphorylation. Co-immunoprecipitation of Fhit and constitutively active Ras^G12V (RasGV) showed that the two molecules were very weakly associated. Previous study showed Fhit partially attenuates RasGV-induced cell growth. These results together suggest Fhit may have a role in regulating RasGV-mediated cell proliferation. To elaborate on previous finding on Fhit association with several Gα proteins, coexpression of Fhit with Gα proteins in HEK 293 cells showed that Fhit has the ability to reduce the Gα_q, Gα_i3, Gα_s, and Gα₁₃-induced ERK phosphorylation. Co-immunoprecipitation used to determine the association of Fhit with MAPK pathway molecules showed association between Fhit and c-Raf in the presence of Gα₁₆, indicating that Fhit may modulate Gα protein-induced ERK phsphorylation through interacting with the MAPK pathway.