Caveolin‐mediated regulation of signaling along the p42/44 MAP kinase cascade in vivo

Abstract

The p42/44 mitogen-activated protein (MAP)-kinase cascade is a well-established signal transduction pathway that is initiated at the cell surface and terminates within the nucleus. More specifically, receptor tyrosine kinases can indirectly activate Raf, which in turn leads to activation of MEK and ERK and ultimately phosphorylation of Elk, a nuclear transcription factor. Recent reports have suggested that some members of p42/44 MAP kinase cascade can be sequestered within plasmalemmal caveolae in vivo. For example, morphological studies have directly shown that ERK-1/2 is concentrated in plasma membrane caveolae in vivo using immunoelectron microscopy. In addition, constitutive activation of the p42/44 MAP kinase cascade is sufficient to reversibly down-regulate caveolin-1 mRNA and protein expression. However, the functional relationship between the p42/44 MAP kinase cascade and caveolins remains unknown. Here, we examine the in vivo role of caveolins in regulating signaling along the MAP kinase cascade. We find that co-expression with caveolin 1 dramatically inhibits signaling from EGF-R, Raf, MEK-1 and ERK-2 to the nucleus. Using a variety of caveolin-1 deletion mutants, we mapped this in vivo inhibitory activity to caveolin-1 residues 32-95. Peptides derived from this region of caveolin 1 also inhibit the in vitro kinase activity of purified MEK-1 and ERK-2. Thus, we show here that caveolin-1 expression can inhibit signal transduction from the p42/44 MAP kinase cascade both in vitro and in vivo. Taken together with previous data, our results also suggest that a novel form of reciprocal negative regulation exists between p42/44 MAP kinase activation and caveolin-1 protein expression, i.e. up-regulation of caveolin-1 protein expression down-modulates p42/44 MAP kinase activity (this report) and up-regulation of p42/44 MAP kinase activity down-regulates caveolin-1 mRNA and protein expression.

Caveolin-3 expression and caveolae are required for isoflurane-induced cardiac protection from hypoxia and ischemia/reperfusion injury

“…Caveolins, the structural components of caveolae, can function as chaperones and provide direct temporal and spatial regulation with numerous cardio-protective signaling molecules via their scaffolding domain including endothelial nitric oxide synthase (eNOS), Src, PKC, Gprotein α, PI3K, and ERK1/2 [16,38,40]. Interestingly, caveolins can inhibit the activity of some of these signaling proteins such as eNOS and ERK1/2 [41][42][43]. However, at the same time caveolins can promote signaling via enhanced receptor-effector coupling or enhanced receptor affinity when caveolins are up regulated or overexpressed [44,45].…”

Loss of Caveolin-1 Gene Expression Accelerates the Development of Dysplastic Mammary Lesions in Tumor-Prone Transgenic Mice

“…As caveolin-1 has been previously implicated as a negative regulator of Jak-2/STAT5a signaling and as a tonic inhibitor of the p42/44 MAP kinase cascade (Engelman et al, 1998a), we first evaluated the activation state of these pathways by using a panel of phospho-specific antibody probes. Figure 8A shows that the levels of total STAT5a and phospho-STAT5a remain unchanged in PyMT/ Cav-1 (Ϫ/Ϫ) samples.…”

“…The hypercellular lung phenotype observed in Cav-1 null mice also suggests that one or more cell types are experiencing a disruption in cell cycle regulation. Mechanistic insight into the relationship between caveolin-1 and cellular proliferation has been provided by experiments that show that caveolin-1 and the Ras-p42/44 MAP kinase cascade undergo a form of reciprocal regulation: 1) down-regulation of caveolin-1 expression by using an antisense approach leads to constitutive ERK activation (Galbiati et al, 1998); 2) up-regulation of caveolin-1 downregulates p42/44 MAP kinase activity, as measured using an Elk-luciferase reporter system, as well as by using in vitro reconstitution experiments (Engelman et al, 1998a); and 3) down-regulation of p42/44 MAPK activity by treatment of …”

Growth of hormone-dependent MCF-7 breast cancer cells is promoted by constitutive caveolin-1 whose expression is lost in an EGF-R-mediated manner during development of tamoxifen resistance

“…Examples of kinases shown to be inhibited by this association include amongst others the epidermal-and platelet-derived growth factor receptors (EGFR and PDGFR), several members of the ERK1/2 MAP kinase cascade, heterotrimeric G-proteins and src family tyrosine kinases [14][15][16]. Furthermore, several independent studies have demonstrated a reciprocal interaction between the expression of caveolin-1 and activated components of the ERK1/2 MAP kinase signalling pathway [17][18][19][20]. While, caveolin-1 mRNA and protein has been shown to be present in normal human mammary epithelial cells it has also been reported to be greatly reduced or absent in an extensive range of transformed cells derived from human breast cancers [21][22][23][24].…”