Stress hormones regulate interleukin-6 expression by human ovarian carcinoma cells through a Src-dependent mechanism

Recent studies have demonstrated that chronic stress promotes tumor growth, angiogenesis, and metastasis. In ovarian cancer, levels of the pro-angiogenic cytokine, interleukin 6 (IL-6), are known to be elevated in individuals experiencing chronic stress, but the mechanism(s) by which this cytokine is regulated and its role in tumor growth remain under investigation. Here we show that stress hormones such as norepinephrine lead to increased expression of IL-6 mRNA and protein levels in ovarian carcinoma cells. Furthermore, we demonstrate that norepinephrine stimulation activates Src tyrosine kinase and this activation is required for increased IL-6 expression. These results demonstrate that stress hormones activate signaling pathways known to be critical in ovarian tumor progression.     

GTP‐dependent permeabilized neutrophil secretion requires a freely diffusible cytosolic protein

Guanosine triphosphate (GTP) has been implicated in the regulation of Ca²⁺‐mediated secretion from neutrophils. We further examined the role of GTP in neutrophil secretion using streptolysin O permeabilized cells. We found that, in the presence of GTP, 1.0 μM free Ca²⁺ causes maximum secretion—equivalent to that achieved with 100 μM free Ca²⁺—whereas GTPγS inhibits Ca²⁺‐stimulated secretion. Interestingly, GTP by itself stimulates secretion. These results indicate the existence of a GTP‐regulated mechanism of secretion in neutrophils that requires GTP hydrolysis to stimulate secretion in the presence and absence of Ca²⁺. The stimulatory effect of GTP is only observed when GTP is present during permeabilization. Addition of GTP after permeabilization, when the cytosolic contents have leaked out from cells, gives no stimulatory response, implying that the GTP‐dependent secretory apparatus requires at least one cytosolic protein. GTP‐dependent secretion can be reconstituted with crude HL‐60 and bovine liver cytosol. The reconstituting activity binds to GTP‐agarose, suggesting that the cytosolic factor is a GTP‐binding protein or forms a complex with a GTP‐binding protein. However, it is not a member of the rho or rac families of GTPases. By gel filtration chromatography, the secretion‐reconstituting activity eluted at 870 and 200 kDa, but in the presence of GTP, eluted at 120 kDa, indicating that it is part of a high‐molecular‐weight complex that dissociates in the presence of GTP. Retention of adenosine diphosphate‐ribosylation factor (ARF) in permeabilized cells and insensitivity of the cytosolic reconstituting activity to brefeldin A led to our speculation that ARF6 may be the GTPase involved in GTP‐dependent secretion, and that activity from a BFA‐insensitive ARF6 guanine nucleotide exchange factor reconstitutes secretion. J. Cell. Biochem. 80:37–45, 2000. © 2000 Wiley‐Liss, Inc.     

Cdk5/p35 expression in the mouse ovary

Cyclin-dependent kinase 5 (Cdk5) is primarily associated with brain development but it is also implicated in lens and muscle differentiation. We found that Cdk5 is also expressed in mouse ovary, and explored the possibility that it plays a role in that tissue. We show by Western blotting and immunohistochemistry that the known Cdk5 activator, p35, is also present in the mouse ovary. Cdk5 and p35 were detected in oocytes at all stages of the follicle. While Cdk5 was present in the cytoplasm and nucleus of the oocyte, p35 was observed only in the cytoplasm. Both proteins were detected in the cytoplasm of luteinized cells in the corpus luteum. Immunoprecipitation and histone H1 kinase assays revealed that they form an ovarian complex with considerable kinase activity. Phosphorylation assays showed that several ovarian proteins are substrates for Cdk5/p35 in vitro. Together our findings suggest that p35-associated Cdk5 activity plays an important role in the ovary, where it may regulate cell differentiation and apoptosis as it does in the brain.     

Chronic stress promotes tumor growth and angiogenesis in a mouse model of ovarian carcinoma

Stress can alter immunological, neurochemical and endocrinological functions, but its role in cancer progression is not well understood. Here, we show that chronic behavioral stress results in higher levels of tissue catecholamines, greater tumor burden and more invasive growth of ovarian carcinoma cells in an orthotopic mouse model. These effects are mediated primarily through activation of the tumor cell cyclic AMP (cAMP)-protein kinase A (PKA) signaling pathway by the beta(2) adrenergic receptor (encoded by ADRB2). Tumors in stressed animals showed markedly increased vascularization and enhanced expression of VEGF, MMP2 and MMP9, and we found that angiogenic processes mediated the effects of stress on tumor growth in vivo. These data identify beta-adrenergic activation of the cAMP-PKA signaling pathway as a major mechanism by which behavioral stress can enhance tumor angiogenesis in vivo and thereby promote malignant cell growth. These data also suggest that blocking ADRB-mediated angiogenesis could have therapeutic implications for the management of ovarian cancer.