Cooperation between Myc and YY1 provides novel silencing transcriptional targets of alpha3beta1- integrin in tumor cells.

We show that human osteosarcoma cells (Saos-2) have downregulation of a3b1-integrin compared to normal bone cells; this was further described in human osteosarcomas and in a primary murine sarcoma. The a3gene was silenced in Saos-2 cells causing a low expression of a3b1- integrin and reduction in collagen attachment with increasing migratory capacity. Chromatin immunoprecipitation assay performed on a3prom oter established that Myc and Yin Yang protein (YY1) cooperate in tandem to downregulate the a3gene. This silencing mechanism involves the binding of Myc and YY1 to DNA and formation of complexes among Myc/Max, YY1, CREBbinding protein and deacetylation activity. The promoter containing deletions of E-boxes or YY1 cassettes failed to downregulate the transcription of a reporter gene as well as the inhibition of deacetylation activity. Overexpression of both Myc and YY1 was necessary to determine the a3- integrin promoter downregulation in normal osteoblasts. This downregulation of a3b1-integrin can contribute to the acquisition of a more aggressive phenotype. YY1 regulated negatively the Myc activity through a direct interaction with the Myc/Max and deacetylase complexes. This represents a novel silencing mechanism with broad implications in the transcription machinery of tumours