Secretion and transport of mouse epididymal proteins after injection of 35S-methionine

Abstract

The presence of epididymal secretory proteins in crude luminal fluids of the epididymis of mice was investigated at varying times after i.v. injection of 35S-methionine or after incubation of epididymal minces with 35-S-methionine. The amount of label incorporated into luminal proteins after in vivo injection was not significantly different at 4, 8, 12, and 16 h. The quantity of labeled proteins in the crude luminal fluids of Regions 1-3 (caput) was about two and four times higher than in Regions 4 (corpus) and 5 (cauda), respectively. Increasing the dosage of 35S-methionine strongly increased the amount of labeled protein present. Approximately half of the labeled protein present in the epididymis was found in the luminal fluid. Polyacylamide gel electrophoresis revealed comparable patterns of proteins at 8 h after injection of isotope or after a 5-h in vitro incubation of minced epididymal tissues with isotype. The protein patterns from the five regions, however, were markedly different from each other and highly characteristic. Two proteins (25 kDa and 18 kDa) were found in crude luminal fluids of Regions 2 and 3 eight hours after in vivo injection, but not in Regions 4 and 5. One protein (29 kDa) was found in high amounts in Regions 4 and 5 eight hours after injection. Five days after injection, the three proteins were found in Regions 4 and 5. However, the 25-kDa protein was present in reduced amount, whereas the 18- and 29-kDa proteins accumulated in caudal fluid. Synthesis and secretion of the 18- and 25-kDa proteins were highly androgen-dependent, while synthesis and secretion of the 29-kDa protein was less androgen dependent. The present study demonstrates that after injection of labeled methionine, the secretion, transport, and fate of epididymal secretory proteins can be followed.