Convergence and Divergence of the Signaling Pathways for Insulin and Phosphoinositolglycans

Table 1 Effect of treatment of control and trypsin/salt-treated adipocytes with PIG-P, PLC, and sulfonylureas on tyrosine phosphorylation of caveolin and lipogenesis

Assay	Tyrosine Phosphorylation of Caveolin		Lipogenesis
Cells	Control	Trypsin/salt-treated	Control	Trypsin/salt-treated
Basal	1 ± 0.2	0.8 ± 0.2	1 ± 0.1	1.3 ± 0.1
PIG-P (0.5 µm)	3.1 ± 0.4	1.0 ± 0.2	5.9 ± 1.1	1.5 ± 0.3
PIG-P (2 µm)	5.5 ± 0.8	1.2 ± 0.3	10.9 ± 1.5	1.7 ± 0.3
PIG-P (5 µm)	7.5 ± 0.9	1.3 ± 0.4	16.8 ± 1.9	2.1 ± 0.3
PIG-P (10 jam)	11.9 ± 2.0	1.8 ± 0.5	23.4 ± 2.4	2.5 ± 0.4
PI-PLC (1 µU/ml)	1.6 ± 0.4	1.1 ± 0.3	1.8 ± 0.5	1.2 ± 0.3
PI-PLC (3 µU/ml)	2.0 ± 0.4	0.9 ± 0.1	3.5 ± 0.7	1.3 ± 0.2
PI-PLC (10 µU/ml)	2.9 ± 0.5	1.5 ± 0.3	4.7 ± 0.9	2.0 ± 0.4
PC-PLC (100 µU/ml)	1.2 ± 0.3	1.1 ± 0.3	1.1 ± 0.2	1.4 ± 0.2
Glimepiride (1 µm)	1.4 ± 0.3	0.9 ± 0.4	2.8 ± 0.5	1.1 ± 0.2
Glimepiride (5 µm)	2.4 ± 0.3	1.1 ± 0.3	4.7 ± 0.4	1.5 ± 0.3
Tolbutamide (1 mM)	0.9 ± 0.1	0.8 ± 0.2	0.9 ± 0.1	1.1 ± 0.2

Untreated (control) or trypsin/salt-treated (100 µg/ml trypsin, 0.5 M NaCl) adipocytes (1 × 10⁶ cells/ml) were incubated (37^°C) with the indicated concentrations of PIG-P for 20 min or PI/PC-specific PLC for 40 min or glimepiride/tolbutamide for 2 hr. From one portion of cells, detergent-insoluble complexes were prepared and analyzed for tyrosine-phosphorylated caveolin by immunoprecipitation with anti-caveolin antibodies and subsequent immunoblotting with anti-phosphotyrosine antibodies and [¹²⁵Ilprotein A (see Materials and Methods). Another portion of cells was assayed for lipogenesis. Each value represents the stimulation factor (above basal) ± SD of three different adipocyte preparations and incubations with caveolin phosphorylation determinations in duplicate and lipogenesis determinations in quadruplicate.

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