PROCESSING OF EPIDERMAL GROWTH-FACTOR IN THE RAT SUBMANDIBULAR-GLAND BY KALLIKREIN-LIKE ENZYMES

Epidermal growth factor (EGF) is synthesized as a precursor which is p rocessed intracellularly to a 6 kDa EGF in the rat submandibular gland . This gland contains very high amounts of kallikrein-like enzymes, an d the purpose of the present study was to examine whether any of five such enzymes, rK1, rK2, rK7, rK9 or rK10, can process the rat EGF prec ursor. Molecular weight forms of EGF, that were N- or C-terminally ext ended compared to submandibular gland EGF were obtained from rat urine . These extended forms of EGF were incubated with each of the enzymes for 24 h at 37 degrees C. Two enzymes, rK7 and rK10, were able to clea ve N- and C-terminally extended EGF, releasing a form of EGF which elu ted similarly to submandibular gland EGF upon gel filtration, and whic h was recognized both by antibodies against rat EGF and by the EGF rec eptor. One enzyme, rK1, cleaved C-but not N-terminally extended EGF. N either rK2, nor rK9 cleaved the extended forms of EGF. In previous imm unohistochemical studies rK1, rK7 and rK10 have all been demonstrated in the EGF containing cells of the rat submandibular gland. EGF and rK 1 are also synthesized in the rat kidney but the present study demonst rated that EGF and rK1 are not colocalized in this organ. Based on the cleavage of the extended forms of rat EGF by rK1, rK7 and rK10 and on the fact that the enzymes are abundant and colocalized with EGF in th e rat submandibular gland, we suggest that rK1, rK7 and rK10 can be in volved in the processing of the EGF precursor in the rat submandibular gland.