PI 3′K activity is higher in mouse than in human plasma cell tumors.
(A) Various cell lines were serum starved for 2 hours and either left untreated or stimulated with IGF-I for 10 minutes. Equivalent cell lysates were immunoprecipitated with anti–IRS-2 (for PCT lines) or anti–IRS-1 (for MM lines) and subjected to a PI 3′K activity assay as previously described.38 NIH 3T3 fibroblasts were serum starved overnight and treated with PDGF-BB (100 ng/mL) for 10 minutes. Cell lysates from NIH 3T3 cells were immunoprecipitated with anti–PDGF-βR and included in the assay as a positive control. (B) Cells were similarly treated as in panel A and equivalent amounts of cell lysates were immunoprecipitated with anti-pTyr. Washed immunoprecipitates were subjected to a PI 3′K activity assay. The PIP3 products of PI 3′K activation are indicated.
