Summary of Research Project Results under JSPS FY2001
"Research for the Future Program"

1.Research Institution@Kobe University
2.Research Area@Life Sciences
3.Research Field@Cellular Signaling
4.Term of Project@FY 1998 ` FY 2001
5.Project Number@98L00301
6.Title of Project@Downstream Effectors of PI3-kinase in Insulin Action

7.Project Leader
Name Institution,Department Title of Position
Masato, Kasuga Kobe University, Graduate School of Medicine Professor

8.Core Members

Names Institution,Department Title of Position
Ogawa, Wataru Kobe University, Graduate School of Medicine Assistant Professor
Tetsuya, Noguchi Kobe University, Graduate School of Medicine Lecturer
Satoshi, Miyata Kobe University, Graduate School of Medicine Assistant Professor

9.Summary of Research Results

We examined a role of PI3-kinase and its downstream effectors in insulin action in vivo and in vitro.
Although we have already shown that PI3-kinase is necessary for metabolic effects of insulin in vitro, physiological importance of PI3-kinase in insulin actions in vivo remained obscure. Therefore, we introduced a dominant negative PI3-kinase, a mutant p85(p85) lacking the binding site for the catalytic subunit , with the use of adenovirus-mediated gene transfer in mice liver. p85-infused mice displayed marked increase in blood glucose in response to oral glucose tolerance test. Furthermore, p85-infused mice showed increased plasma insulin levels in both fasted and fed states. These results indicate that PI3-kinase activity in liver plays an important role in glucose homeostasis and insulin actions in vivo.
We also examined roles of downstream effectors of PI3-kinase, Akt and atypical PKC (PKC) using adenovirus vectors encoding constitive active or dominant negative mutant of these molecules, in vitro. We found that Akt is necessary for insulin-dependent protein synthesis, glycogen synthase activation and phosphorylation of PDE3B. On the other hand, our data suggested that PKC is involved in insulin-dependent increase of mRNA of SREBP-1 in hepatocytes and insulin-stimulated glucose transport in adipocytes.
Finally, we examined a role of PKC in insulin action in vivo. Since PKC knockout mice were embryonic lethal, we generated liver-specific PKC knockout mice. These mice exhibited normal glucose levels in both fasted and fed states, however plasma insulin concentrations were lower in these mice. Furtheremore, in these mice, mRNA levels of SREBP-1 and triglyceride content in the liver were significantly decreased. These data suggest that PKC in the liver plays an important role in insulin action in vivo.
Thus, we clarified important roles of PI3-kinase, Akt and PKC in insulin action both in vivoand in vitro.

10.Key Words

(1)PI3-kinaseA(2)Akt(PKB)A(3)atypical PKC
(4)insulin signalingA(5)adenovirus vectorA(6)tissue-specific knockout mice
(7)diabetes mellitusA(8)insulin resistance