SH3 domain of the XXXX 3-kinase regulatory subunit is responsible for the formation of a sequestration complex with @entity10175 .

@entity1 @entity53080 @entity10175 @entity2690 @entity10241 @entity4357 @entity8569
Class IA @entity4357 3-kinase (PI 3-kinase), which is composed of a 110kDa catalytic subunit and a regulatory subunit, plays a key role in most insulin dependent cellular responses. To date, five @entity1 regulatory subunit isoforms have been identified, including two 85kDa proteins ( @entity10241 and @entity8569 ), two 55kDa proteins ( @entity53080 and p55alpha), and one 50kDa protein (p50alpha). In the present study, we overexpressed these recombinant proteins, tagged with green fluorescent proteins (GFP), in CHO-IR cells and investigated intracellular localizations in both the presence and the absence of insulin stimulation. Interestingly, in response to insulin, only @entity10241 and @entity8569 redistributed to isolated foci in the cells, while both were present throughout the cytoplasm in quiescent cells. In contrast, @entity53080 s accumulated in the perinuclear region irrespective of insulin stimulation, while p50alpha behaved similarly to control GFP. Immunofluorescent antibodies against endogenous @entity10175 revealed @entity10175 to be co-localized in the @entity10241 foci in response to insulin. As both @entity2690 catalytic subunits were absent from these foci on immunofluorescence study, only @entity10241 and @entity10175 were suggested to form a sequestration complex in response to insulin. To determine the domain responsible for @entity10175 complex formation, we prepared and overexpressed the SH3 domain deletion mutant of @entity10241 in CHO-IR cells. This mutant failed to form foci, suggesting the SH3 domain of regulatory subunits to be responsible for formation of the @entity10241 - @entity10175 sequestration complex. In conclusion, our study revealed the SH3 domain of PI 3-kinase to play a critical role in intracellular localizations, including formation of foci with @entity10175 in response to insulin.
