Effect of transglutaminase substrates and polyamines on the cellular sequestration and processing of follicle-stimulating hormone by rat Sertoli cells.

Transglutaminase (TGase) substrates monodansyl cadaverine (MDC, monodansyl-1,5 diaminopentane) and methylamine (MA) and polyamines (PA) were tested for their effects on the cellular processing of radioiodinated human follicle-stimulating hormone (125I-hFSH). Specifically bound 125I-hFSH that could be released from cells during 10-min incubation period with acidified (pH 3.9) Hanks balanced-salt solution was considered membrane-bound unsequestered hormone. The rate at which cells sequestered 125I-hFSH into cellular compartments resistant to acid dissociation depended on the length of time in which cells were incubated with hormone. Cells incubated with 125I-hFSH for 15, 60, and 120 min had half-lives of sequestration of 26, 55 and 67 min respectively. One hundred-micromolar MDC inhibited degradation of 125I-hFSH as measured by the presence of radioactivity in the medium that was soluble in trichloroacetic acid. The rate of sequestration was never slower than that of controls, indicating that MDC did not decrease the ability of Sertoli cells to sequester 125I-hFSH. Despite these two observations, radioactivity associated with cells (acid-resistant radioactivity) was lower in cells treated with MDC than in controls. No effect of MDC on specific binding of 125I-hFSH was observed. Similar results were observed with MA, albeit at higher levels (0.0025-0.0425 M), consistent with their relative potency to inhibit TGase activity. Polyamines, spermine, and putrescine also decreased cell-associated radioactivity despite decreasing degradation of hFSH. TGase substrates (MDC, MA, PA) prevented entry of sequestered 125I-hFSH into the degradative pathways of Sertoli cells. These data suggest that transglutamination may influence the fate of sequestered FSH in Sertoli cells but not the rate at which sequestration occurs.