PHAS-I phosphorylation in response to foetal bovine serum (FBS) is regulated by an ERK1/ERK2-independent and rapamycin-sensitive pathway in 3T3-L1 adipocytes.

The phosphorylation state of PHAS-I is thought to be important in the regulation of protein synthesis initiation. PHAS-I phosphorylation significantly increases in response to growth factors and insulin. ERK1/ERK2 have previously been implicated as PHAS-I kinases. Present work utilised a specific phosphorothioate oligonucleotide antisense strategy against ERK1/ERK2 to determine whether ERK1/ERK2 mediate FBS-stimulated PHAS-I phosphorylation in vivo. Depleting > 90% of cellular ERK1/ERK2 had no effect on FBS-stimulated PHAS-I phosphorylation. However, treatment of cells with a specific p70S6k pathway inhibitor, rapamycin, markedly attenuated FBS-stimulated PHAS-I phosphorylation. These results indicate that PHAS-I phosphorylation in response to FBS occurs through an ERK1/ERK2-independent and rapamycin-sensitive pathway in 3T3-L1 adipocytes.