Multifunctional adaptor proteins may have divergent actions in early versus late phases of cancer progression, playing both tumor-suppressing and tumor-promoting roles in a context-dependent manner. One such protein is the adaptor and caveolar coat protein caveolin-1, which is an essential structural constituent of plasma membrane caveolae (for a review, see [1,2]). The cellular localization of caveolin-1 is not limited to caveolae in all cells [3], and it exhibits diverse functions that go beyond its well-characterized role as a component of the caveolar coat (for a review, see [4]). Caveolin-1 was implicated in tumorigenesis because its expression is suppressed by oncogenic transformation, and little or no expression of caveolin-1 was initially found in various human tumors and cancer cell lines [5]. In addition, caveolin-1 has well-established growth-inhibitory properties, and it has been suggested to act as a tumor-suppressor protein [5]. However, a general tumor suppressor action cannot easily be reconciled with the fact that, in many other cancer cell lines and tumor specimens, the expression of caveolin-1 is high [6]. Furthermore, a positive correlation was often noted between the expression of caveolin-1 and the tumor cell grade and progression stage; in certain studies, the expression of caveolin-1 could be used to independently predict poor disease prognosis [6].

How can the divergent, cell type- and tumor stage-dependent changes in caveolin-1 be explained? Previous studies have indicated that in addition to its growth-inhibitory action, under certain circumstances caveolin-1 acts as a survival-promoting protein [7-14]. The differential expression of caveolin-1 in various tumor cells and specimens may thus be explained by the ability of caveolin-1 to exert both antiproliferative and pro-survival effects. It was previously hypothesized that, during the early stages of cancer progression (when rapid proliferation is essential for clonal expansion), expression of caveolin-1 is down-regulated, thus suppressing its growth-inhibitory actions. Conversely, during the late, advanced stages of the disease (when survival and stress resistance are paramount), expression of caveolin-1 is up-regulated and it plays a pro-survival role [6,15]. In the following sections we shall re-evaluate this hypothesis in view of recent evidence that relates the expression and function(s) of caveolin-1 to cancer progression and tumor cell survival.

Was this article helpful?

0 0
10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook

Post a comment