In this study, we addressed the effects of selected stress hormones on ovarian cancer invasion, which is a critical component of the metastatic cascade. Our data show that physiologically relevant concentrations of norepinephrine and epinephrine can significantly enhance the capacity of ovarian tumor cells to invade the extracellular matrix that is characteristic of the basement membrane. These effects are mediated via β-adrenergic receptors on cancer cells, which can enhance production of MMP-2 and MMP-9. Changes in MMP expression facilitate ovarian cancer cell penetration of extracellular matrix, and pharmacologic blockade of those effects can inhibit catecholamine-mediated increases in tumor cell invasion. Furthermore, a β-adrenergic agonist (isoproterenol) promoted in vivo tumor growth and infiltration. In addition to documenting a novel mechanism by which stress biology might effect the pathogenesis of ovarian cancer, these data identify two key molecular mediators of such effects (β-adrenergic receptors and MMP expression).
The effects observed here take place at physiologically relevant concentrations of catecholamines. Basal circulating levels of norepinephrine range between 10 pmol/L and 1 nmol/L, with stress increasing these levels to 100 nmol/L (46
). Circulating epinephrine levels range from 1 to 10 pmol/L, and increase up to 10 nmol/L under stress (46
). Stress can also increase tissue catecholamine levels in the ovary via increased sympathetic activity, which has been shown to trigger precystic follicles (47
). However, in addition to the sympathetic innervation, the primate ovary contains the endogenous enzymatic machinery necessary for catecholamine biosynthesis (51
). As a result, ovarian tissue levels of catecholamines can substantially exceed those in plasma (22
). Therefore, the in vitro
doses of catecholamines used in our experiments cover the spectrum of stress and nonstress levels that the tumor cells would be exposed to in vivo
and are consistent with doses that promote biological effects in other in vitro
). Thus, the present data suggest that catecholamine effects on ovarian cancer invasive potential occur at physiologically relevant levels of those hormones.
The ability to invade extracellular matrices plays an important role in metastasis and in development of blood flow to tumors. The process of tumor cell penetration of the host basement membrane consists of attachment, matrix dissolution, motility, and penetration (58
). MMPs play a key role in these dynamics by degrading components of the extracellular matrix, such as collagen, laminins, fibronectins, elastins, and the protein core of proteoglycans (39
). Given their destructive potential, MMPs are normally expressed only when and where they are needed to support physiologic processes, such as embryonic development, wound healing, and placental development (59
). Aberrant expression of MMPs contributes to several pathologic conditions, including tumor cell invasion and metastasis. MMPs associated with ovarian carcinomas include MMP-2 and MMP-9 (32
). MMP-2 is the primary gelatinolytic MMP secreted by ovarian cancer cells (32
) and MMP-9 contributes to the angiogenic switch that occurs during carcinogenesis (61
). Recently, Huang et al. (63
) have shown that host-derived MMP-9 expression plays a critical role in angiogenesis and progressive growth of human ovarian tumors in mice. We have previously shown the critical role of specific MMPs in the in vitro
matrix remodeling by ovarian cancer cells (31
). The present data show that physiologic stress hormones can significantly enhance the expression and activity of these key MMPs by ovarian cancer cells.
These data provide the first indication that MMPs might play a role in stress hormone–mediated changes in ovarian cancer cell function. Previous studies have linked hormone dynamics to MMP production by other cell types. Yang et al. (29
) examined the effects of stress on MMP levels using a blister chamber wound model on UV-B–exposed human forearm skin. In their study, plasma norepinephrine levels were correlated with high MMP-2 protein levels in damaged dermal tissue. Recent studies in mice also suggest that psychological stress can elevate MMP activity. Wu et al. stressed mice by social isolation and found increased expression of mRNA for MMP-2, MMP-9, matrix-type MMP-1, and urokinase-type plasminogen activator in colon tumors and liver tissues in stressed versus control mice (30
). The present study shows similar effects in the context of ovarian cancer and it extends those findings to show the functional significance of increased MMP expression in facilitating tumor cell invasion of basement membrane-like structures. It is possible that other factors may also be involved in stress hormone–stimulated invasion and will be examined in ongoing work in our laboratory.
In summary, our results show that stress hormones can directly increase the invasive potential of ovarian cancer cells via β-adrenergic up-regulation of MMP-2 and MMP-9. In conjunction with previous studies showing β-adrenergic regulation of other molecular processes involved in the metastatic cascade (26
), these results suggest that physiologic catecholamine activity could represent a new target for adjunctive therapies that seek to block metastatic processes during and after primary therapy. Understanding the neuroendocrine influences on cancer growth and progression might allow development of strategies to delay or prevent malignant disease.