Transcriptional activation of c-Fos by constitutively active Gα16QL through a STAT1-dependent pathway

Hematopoietic restrictive Gα16 has long been known to stimulate phospholipase Cβ (PLCβ) and induce mitogen-activated protein kinase (MAPK) phosphorylation. Recently, we have demonstrated that Gα16 is capable of inducing the phosphorylation and transcriptional activation of transcription factors, such as signal transducer and activator of transcription 3 (STAT3) and nuclear factor κB (NFκB). However, the downstream signaling regulation by Gα16 has not yet been documented. In the present study, we have determined the signaling mechanism by which constitutively active Gα16 mediates c-Fos transcriptional activation in human embryonic kidney (HEK) 293 cells. Overexpression of constitutively active Gα16, Gα16QL, resulted in the stimulation of c-Fos transcriptional activation in HEK 293 cells. The participation of PLCβ, c-Src/Janus kinase 2 (JAK2) and extracellular signal-regulated kinase (ERK) signaling pathways in Gα16QL-induced c-Fos transcriptional activation was demonstrated by the use of their specific inhibitors. However, c-Jun N terminal kinase (JNK), p38 MAPK and phosphatidylinositol-3 kinase (PI3K) were not required. Interestingly, the dominant negative mutant of STAT1, but not STAT3, suppressed c-Fos transcriptional activation induced by Gα16QL, implying that STAT1 was involved in this signaling mechanism. To further examine the role of STAT1 in the signaling pathway of Gα16, we demonstrated that Gα16QL was able to induce STAT1 activation. Also, stimulation of adenosine A1 receptor-coupled Gα16 was shown to induce ERK and STAT1 phosphorylations in a concentration-dependent manner. Using selective inhibitors, PLCβ, c-Src/JAK and ERK, but not JNK, p38 MAPK and PI3K, were shown to be involved in Gα16QL-induced STAT1 activation. Collectively, our results demonstrate for the first time that stimulation of Gα16 can lead to STAT1-dependent c-Fos transcriptional activation via PLCβ, c-Src/JAK and ERK pathways.