Janovick J A, Natarajan K, Longo F, Conn P M
Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242-1109.
Endocrinology. 1991 Jul;129(1):68-74. doi: 10.1210/endo-129-1-68.
Calmodulin (CaM) serves as an intracellular Ca2+ receptor in the gonadotrope and appears to mediate GnRH-stimulated gonadotropin release. Recently we have specifically identified three CaM binding proteins of the gonadotrope as calcineurin, caldesmon, and spectrin. Caldesmon (identified by seven polyclonal and a monoclonal antibody, as well as by functional characteristics) appears to be a CaM-regulated, F-actin binding, protein. This 84,000 mol wt component (CaD84) is heat stable and cosediments with F-actin in the absence of Ca2+. In the presence of Ca2+ (greater than 1 microM) this protein disassociates from F-actin and reassociates with calmodulin. We have prepared an antibody which blocks the caldesmon-actin interaction. In the present study, we have loaded this antibody into cells to prevent the (re-)association of caldesmon with F-actin. This treatment synergistically augments the ability of GnRH and other secretogogues (maitotoxin, phorbol myristyl acetate) to stimulate gonadotropin release from the pituitary. This finding, along with the previous observations that GnRH provokes a sufficient rise in intracellular Ca2+ to allow CaM to redistribute and bind proteins which it regulates, suggests a role for caldesmon in GnRH-stimulated gonadotropin release from the pituitary.
钙调蛋白（CaM）在促性腺激素细胞中作为细胞内钙离子受体，似乎介导促性腺激素释放激素（GnRH）刺激的促性腺激素释放。最近，我们已明确鉴定出促性腺激素细胞的三种钙调蛋白结合蛋白，即钙调磷酸酶、钙调素和血影蛋白。钙调素（通过七种多克隆抗体、一种单克隆抗体以及功能特性鉴定）似乎是一种受钙调蛋白调节、与F-肌动蛋白结合的蛋白质。这种分子量为84,000的成分（CaD84）热稳定，在无钙离子的情况下与F-肌动蛋白共沉降。在钙离子存在（大于1微摩尔）时，该蛋白从F-肌动蛋白上解离并与钙调蛋白重新结合。我们制备了一种能阻断钙调素-肌动蛋白相互作用的抗体。在本研究中，我们将这种抗体导入细胞，以防止钙调素与F-肌动蛋白（重新）结合。这种处理协同增强了GnRH和其他促分泌素（ maitotoxin、佛波酯肉豆蔻酸酯）刺激垂体释放促性腺激素的能力。这一发现，连同之前的观察结果，即GnRH引起细胞内钙离子充分升高，使钙调蛋白重新分布并结合其调节的蛋白质，提示钙调素在GnRH刺激垂体释放促性腺激素过程中发挥作用。
