Carystinos G D, Alaoui-Jamali M A, Phipps J, Yen L, Batist G
Lady Davis Institute of the Sir Mortimer B. Davis--Jewish General Hospital and Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada.
Cancer Chemother Pharmacol. 2001;47(2):126-32. doi: 10.1007/s002800000231.
Downregulation of gap junctional intercellular communication (GJIC) has been implicated in carcinogenesis. This is a result of altered expression of connexins, the proteins that mediate GJIC, including connexin 43 (Cx43). Our aim was to evaluate the effect of known inducers of Cx43 on the chemosensitivity of the human neuroblastoma cell line IMR-32 to chemotherapeutic agents.
We examined the effect of dibutyryl-cyclic AMP (db-cAMP) and all-trans-retinoic acid (tRA) on Cx43 and GJIC, glutathione (GSH) and gamma-glutamyl-cysteine-synthetase (gamma-GCS) levels, and glutathione S-transferase (GST) activity. Finally, we performed cell survival assays to measure the response of IMR-32 cells to the chemotherapeutic drugs doxorubicin, melphalan and bis-chloronitrosourea (BCNU), after treatment with db-cAMP and/or tRA.
Exposure to db-cAMP led to the upregulation of GJIC and Cx43 expression and phosphorylation. On the other hand, exposure to tRA led to the upregulation of GJIC but Cx43 expression and phosphorylation were not greatly affected. The combination of both agents was more potent in inducing GJIC in comparison to treatment with db-cAMP or tRA alone. Treatment with db-cAMP, but not with tRA, was associated with a significant increase in the cytotoxic effects of the anticancer drugs doxorubicin, melphalan and BCNU as shown by a decrease in their IC50 values. Concomitant exposure to db-cAMP and tRA, however, had a more pronounced effect on cell sensitization to chemotherapy drugs (particularly doxorubicin) than exposure to db-cAMP or tRA alone. Under the db-cAMP and tRA treatment conditions (which upregulate GJIC and modulate drug response), GSH levels were significantly reduced while the levels of GST and gamma-GCS activities remained unchanged.
This study suggests that GJIC plays a role in cellular drug resistance, and highlights the potential use of GJIC modulators in combination with chemotherapy. Also, this is the first study exploring the ability of both db-cAMP and tRA to enhance cell chemosensitivity.
间隙连接细胞间通讯（GJIC）的下调与致癌作用有关。这是连接蛋白表达改变的结果，连接蛋白是介导GJIC的蛋白质，包括连接蛋白43（Cx43）。我们的目的是评估已知的Cx43诱导剂对人神经母细胞瘤细胞系IMR-32对化疗药物的化学敏感性的影响。
我们研究了二丁酰环磷腺苷（db-cAMP）和全反式维甲酸（tRA）对Cx43和GJIC、谷胱甘肽（GSH）和γ-谷氨酰半胱氨酸合成酶（γ-GCS）水平以及谷胱甘肽S-转移酶（GST）活性的影响。最后，我们进行了细胞存活试验，以测量IMR-32细胞在用db-cAMP和/或tRA处理后对化疗药物阿霉素、美法仑和双氯亚硝基脲（BCNU）的反应。
暴露于db-cAMP导致GJIC上调以及Cx43表达和磷酸化增加。另一方面，暴露于tRA导致GJIC上调，但Cx43表达和磷酸化未受到显著影响。与单独用db-cAMP或tRA处理相比，两种药物联合使用在诱导GJIC方面更有效。用db-cAMP处理而非tRA处理，与抗癌药物阿霉素、美法仑和BCNU的细胞毒性作用显著增加有关，表现为它们的IC50值降低。然而，与单独暴露于db-cAMP或tRA相比，同时暴露于db-cAMP和tRA对细胞对化疗药物（特别是阿霉素）的致敏作用更明显。在db-cAMP和tRA处理条件下（上调GJIC并调节药物反应），GSH水平显著降低，而GST和γ-GCS活性水平保持不变。
本研究表明GJIC在细胞耐药中起作用，并突出了GJIC调节剂与化疗联合使用的潜在用途。此外，这是第一项探索db-cAMP和tRA增强细胞化学敏感性能力的研究。
