Tumor necrosis factor alpha (TNF) suppresses cAMP response element (CRE) activity and nuclear CRE binding protein in MA-10 mouse Leydig tumor cells.

TNF is known to suppress gonadotropin-induced steroid secretion by Leydig cells. However, the mechanisms by which this occurs are largely unknown. Because expression of many steroidogenic proteins is regulated by the PKA pathway, effects of TNF on CRE activity were examined using MA-10 mouse Leydig tumor cells. The cells were transfected with a CRE-luciferase construct, and stimulated with either LH or 8Br-cAMP in the presence or absence of TNF. TNF suppressed, LH-stimulated and 8Br-cAMP stimulated CRE activity. TNF also suppressed CRE activity stimulated with a PKA expression vector. Further experiments suggested that the effect of TNF on CRE activity was not mediated by the NF-kappaB pathway. TNF did not affect levels of either CREB or phospho-CREB in whole cell lysates; however, TNF decreased both CREB and phospho-CREB in nuclear extracts in a time-dependent manner. The decrease in nuclear CREB is likely to be a major mechanism of the suppressive effects of TNF on steroidogenesis in MA-10 Leydig cells.