Insulin-induced ectodomain shedding of heparin-binding epidermal growth factor-like growth factor in adipocytes in vitro

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is synthesized as a type I transmembrane protein, which is proteolytically cleaved to release a soluble form via members of the a disintegrin and metalloproteinase (ADAM) family of proteolytic enzymes. This study was designed to elucidate the molecular mechanism underlying insulin-induced HB-EGF shedding in adipocytes in vitro. The 3T3-L1 adipocytes with stable expression of alkaline phosphatase (AP)-tagged proHB-EGF (3T3-L1/HB-EGF-AP adipocytes) were developed and AP activities of conditioned media were determined. Using 3T3-L1/HB-EGF-AP adipocytes, we demonstrated that insulin induces HB-EGF shedding in differentiated 3T3-L1 adipocytes in a dose- and time-dependent manner. There is no significant increase in insulin-induced HB-EGF shedding in undifferentiated 3T3-L1 preadipocytes. Studies with metalloprotease inhibitors suggested that insulin-induced HB-EGF shedding in adipocytes is mediated at least in part via ADAM17. Treatment with recombinant HB-EGF results in a dose- and time-dependent increase in HB-EGF shedding in adipocytes, which is significantly suppressed by pharmacologic blockade of ADAM17 (P < 0.01). Moreover, insulin-induced HB-EGF shedding in adipocytes is significantly inhibited by AG1478, an EGF receptor antagonist (P < 0.01). This study provides in vitro evidence that insulin induces HB-EGF shedding in 3T3-L1 adipocytes. Our data also suggest the role of ADAM17 in insulin-induced HB-EGF shedding in adipocytes.