IL-1beta-induced nitric oxide release from insulin-secreting beta-cells: further evidence for the involvement of GTP-binding proteins.
Recently, we have demonstrated regulatory roles for G-proteins (e.g., H-Ras) in IL-1beta induced NO release from HIT-T15 cells. Herein, we report a similar regulatory mechanism for IL-1beta induced NO release from RIN5F and INS-1 cells. Our data indicate that functional inactivation of Ras, either by Clostridial toxins or by specific inhibitors of Ras function, results in a significant inhibition in IL-1beta induced NO release, suggesting that activation of specific G-proteins is essential for IL-1beta induced NO release. In the present study, we report possible loci where IL-1beta treatment might result in functional activation of these G-proteins. For example, IL-1beta treatment resulted in significant reduction in (high-and low-affinity) GTPase activities in lysates derived from normal rat islets; such a scenario might lead to retention of candidate G-proteins in GTP-bound, active conformation. Further, IL-1beta treatment increased the G-protein carboxyl methyl transferase activity as well as carboxyl methylation of endogenous beta-cell proteins; such a modification has been shown to increase the membrane association and interaction of these G-proteins with their respective effector proteins. Also, we report immunologic localization of H-Ras regulatory proteins including its nucleotide exchange factor (GRF-1) and its effector protein (eg., Raf-1) in isolated beta-cells. Together, our data indicate localization, and regulation by IL-1beta, of specific enzymes that are critical to activation of G-proteins. Based on these preliminary findings, we propose a model for the involvement of G-proteins in IL-1beta induced NO release and subsequent demise of the pancreatic beta-cell.
Tannous
M
M
Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48202, USA.
Veluthakal
R
R
Amin
R
R
Kowluru
A
A
D000818:Animals; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D007375:Interleukin-1 / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014407:Tumor Cells, Cultured
D007375:Interleukin-1; D009569:Nitric Oxide; D019204:GTP-Binding Proteins