Grima J, Pineau C, Bardin C W, Cheng C Y
The Population Council, Center for Biomedical Research, New York, NY 10021.
Mol Cell Endocrinol. 1992 Nov;89(1-2):127-40. doi: 10.1016/0303-7207(92)90219-v.
Clusterin, alpha 2-macroglobulin and testins are three novel Sertoli cell proteins whose physiological functions may be related to cell-cell interactions in the seminiferous epithelium of the testis. We have demonstrated the biosynthesis of clusterin, alpha 2-macroglobulin, and testins by Sertoli cells in vitro using pulse-chase labeling analysis. For clusterin, two precursors with an apparent molecular weight (M(r)) of 72,000 (PH) and 66,000 (PL) were detected in the Sertoli cell cytosol in addition to the alpha (M(r) 43,000) and beta (M(r) 35,000) subunits of the mature protein. However, the precursors were not secreted into the medium since only the alpha and beta subunits of clusterin were detected. For alpha 2-macroglobulin and testins, no precursor molecules were detected either in the Sertoli cell cytosol or culture medium. The polarized secretory pattern of these proteins and their regulation by follicle stimulating hormone (FSH) and testosterone (T) were examined using a bicameral culture chamber that mimics the in vivo physiological conditions. Clusterin was secreted almost exclusively into the apical chamber of the bicameral culture unit with an apical:basal ratio of 30:1. In contrast, alpha 2-macroglobulin and testins had an apical:basal ratio of 1:1 and 1.5:1, respectively. Thus, the polarized secretory pattern for clusterin is different from alpha 2-macroglobulin and testins. It was noted that FSH and T, the known Sertoli cell regulators, did not affect the secretion of either clusterin or alpha 2-macroglobulin. Due to the morphological intimacy between Sertoli cells and germ cells in the adluminal compartment of the testis, the effects of germ cell-conditioned medium were investigated. Addition of germ cell-conditioned medium (1-30 micrograms protein) to the apical chamber of the bicameral culture unit caused a dose-dependent inhibition of clusterin and testins apical secretion and a slight but statistically significant stimulation of their basal secretion. In contrast, the secretion of alpha 2-macroglobulin by Sertoli cells was stimulated both apically and basally. These observations suggest that germ cell-conditioned medium contains a biological factor(s) that differentially regulates the bidirectional secretion of Sertoli cell proteins. These studies therefore reveal the complicated regulatory processes involved in cell-cell interactions in the seminiferous epithelium.
簇集蛋白、α2-巨球蛋白和睾丸抑制素是三种新发现的支持细胞蛋白，其生理功能可能与睾丸生精上皮中的细胞间相互作用有关。我们通过脉冲追踪标记分析，在体外证实了支持细胞可生物合成簇集蛋白、α2-巨球蛋白和睾丸抑制素。对于簇集蛋白，除了成熟蛋白的α亚基（分子量43,000）和β亚基（分子量35,000）外，在支持细胞胞质溶胶中还检测到两种表观分子量分别为72,000（PH）和66,000（PL）的前体。然而，这些前体并未分泌到培养基中，因为在培养基中仅检测到簇集蛋白的α和β亚基。对于α2-巨球蛋白和睾丸抑制素，在支持细胞胞质溶胶或培养基中均未检测到前体分子。使用模拟体内生理条件的双室培养室，研究了这些蛋白的极化分泌模式及其受促卵泡激素（FSH）和睾酮（T）的调节情况。簇集蛋白几乎完全分泌到双室培养装置的顶室中，顶室与底室的比例为30:1。相比之下，α2-巨球蛋白和睾丸抑制素的顶室与底室比例分别为1:1和1.5:1。因此，簇集蛋白的极化分泌模式与α2-巨球蛋白和睾丸抑制素不同。值得注意的是，已知的支持细胞调节因子FSH和T并未影响簇集蛋白或α2-巨球蛋白的分泌。由于睾丸近腔室中支持细胞与生殖细胞之间存在形态上的紧密联系，因此研究了生殖细胞条件培养基的作用。向双室培养装置的顶室中添加生殖细胞条件培养基（1 - 30微克蛋白质）会导致簇集蛋白和睾丸抑制素顶部分泌呈剂量依赖性抑制，同时其底部分泌受到轻微但具有统计学意义的刺激。相比之下，支持细胞分泌的α2-巨球蛋白在顶室和底室均受到刺激。这些观察结果表明，生殖细胞条件培养基中含有一种生物因子，可差异性调节支持细胞蛋白的双向分泌。因此，这些研究揭示了生精上皮中细胞间相互作用所涉及的复杂调节过程。
