Sugimoto T, Kano J, Ikeda K, Fukase M, Chihara K
Department of Medicine, Kobe University School of Medicine, Japan.
J Bone Miner Res. 1993 Apr;8(4):451-8. doi: 10.1002/jbmr.5650080409.
In osteoblastic UMR-106 cells, 10(-7) M human (h) PTH-related peptide (PTHrP)-(1-34) significantly induced the formation of total inositol phosphates to the same degree as 10(-7) M hPTH-(1-34), confirming that in addition to cAMP-dependent protein kinase (PKA), PTHrP possesses another signal transduction system, calcium/protein kinase C (Ca/PKC). Experiments were therefore performed to characterize the cross talk of these dual-signal transduction systems and its participation in the PTHrP-induced homologous desensitization of cAMP and cytosolic calcium (Cai) response in osteoblasts. Preincubation with 10(-7) M hPTHrP-(1-34) caused homologous desensitization, resulting in a remarkable decrease in cAMP accumulation in response to further exposure to PTHrP. This effect was significant after 2 h pretreament and reached a maximum at 6 h. Pretreatment with the PKC-activating phorbol ester phorbol 12-myristate-13-acetate (PMA, 10(-6) M) for 30 minutes and 6 h caused a significant increase and decrease in cAMP responsiveness to PTHrP, respectively. Pretreatment with calcium ionophores (A23187 or ionomycin, 10(-6) M), not for 30 minutes but for 6 h, caused a significant decrease in cAMP responsiveness to PTHrP. H-7 (an inhibitor of PKC, 50 microM) significantly blocked not only PMA- but also PTHrP-induced desensitization of the cAMP response. PTHrP caused the complete homologous desensitization of an increase in Cai within 30 minutes. Pretreatment with dibutyryl-cAMP (10(-4) M) for 30 minutes caused significant inhibition of the PTHrP-induced increase in Cai, and pretreatment with Sp-cAMPS (10(-4) M), a direct activator of PKA, for 30 minutes completely blocked the PTHrP-induced increase in Cai.(ABSTRACT TRUNCATED AT 250 WORDS)
在成骨样UMR - 106细胞中，10⁻⁷ M人（h）甲状旁腺激素相关肽（PTHrP） - （1 - 34）诱导总肌醇磷酸的形成，其程度与10⁻⁷ M hPTH - （1 - 34）相同，这证实了除了环磷酸腺苷（cAMP）依赖性蛋白激酶（PKA）外，PTHrP还拥有另一种信号转导系统，即钙/蛋白激酶C（Ca/PKC）。因此进行了实验，以表征这些双信号转导系统的相互作用及其在成骨细胞中PTHrP诱导的cAMP和胞质钙（Cai）反应同源脱敏中的参与情况。用10⁻⁷ M hPTHrP - （1 - 34）预孵育会导致同源脱敏，导致再次暴露于PTHrP时cAMP积累显著减少。这种效应在预处理2小时后显著，6小时时达到最大值。用蛋白激酶C激活剂佛波酯佛波醇12 - 肉豆蔻酸酯 - 13 - 乙酸酯（PMA，10⁻⁶ M）预处理30分钟和6小时，分别导致对PTHrP的cAMP反应性显著增加和降低。用钙离子载体（A23187或离子霉素，10⁻⁶ M）预处理6小时（而非30分钟），导致对PTHrP的cAMP反应性显著降低。H - 7（一种蛋白激酶C抑制剂，50 μM）不仅显著阻断了PMA诱导的，也阻断了PTHrP诱导的cAMP反应脱敏。PTHrP在30分钟内导致Cai增加的完全同源脱敏。用二丁酰 - cAMP（10⁻⁴ M）预处理30分钟导致PTHrP诱导的Cai增加受到显著抑制，用PKA直接激活剂Sp - cAMPS（10⁻⁴ M）预处理30分钟完全阻断了PTHrP诱导的Cai增加。（摘要截断于250字）
