Identification of intracellular cavin target proteins reveals cavin-PP1alpha interactions regulate apoptosis

Abstract

Caveolae are specialized domains of the plasma membrane. Formation of these invaginations is dependent on the expression of Caveolin-1 or -3 and proteins of the cavin family. In response to stress, caveolae disassemble and cavins are released from caveolae, allowing cavins to potentially interact with intracellular targets. Here, we describe the intracellular (non-plasma membrane) cavin interactome using biotin affinity proteomics and mass spectrometry. We validate 47 potential cavin-interactor proteins using a cell-free expression system and protein-protein binding assays. These data, together with pathway analyses, reveal unknown roles for cavin proteins in metabolism and stress signaling. We validated the interaction between one candidate interactor protein, protein phosphatase 1 alpha (PP1α), and Cavin-1 and -3 and show that UV treatment causes release of Cavin3 from caveolae allowing interaction with, and inhibition of, PP1α. This interaction increases H2AX phosphorylation to stimulate apoptosis, identifying a pro-apoptotic signaling pathway from surface caveolae to the nucleus.

A role for caveola‐forming proteins caveolin‐1 and CAVIN1 in the pro‐invasive response of glioblastoma to osmotic and hydrostatic pressure

“…24 Lastly, the disassembly and flattening of caveolae in response to membrane stretch allows the release of cavins to signal intracellularly (including in the nucleus). 6,7,25 In the present study, we did not observe major effects of hypo-osmotic treatment on matrix protease production or EMT marker expression. Hypo-osmotic stress has been used at various intensities for limited amounts of time in other documented experiments testing the role of caveolae in mechano-protection.…”

“…It is also proposed that caveolae mediate the internalization of damaged membrane areas . Lastly, the disassembly and flattening of caveolae in response to membrane stretch allows the release of cavins to signal intracellularly (including in the nucleus) …”

Caveolae and lipid sorting: Shaping the cellular response to stress

“…The major proteins we will discuss are the cavins, but it is important to note that in model systems, caveolins also show a lipid-concentrating ability (Epand et al, 2005; Wanaski et al, 2003). Importantly for this discussion, as peripheral membrane proteins, cavins, unlike caveolins, can dissociate from the cytoplasmic surface of caveolae in response to stresses (McMahon et al, 2019; Sinha et al, 2011), and so lipid interactions can be regulated. Cavins bind PtdIns(4,5)P 2 via a basic domain in their first helical region, HR1 (Kovtun et al, 2014).…”

“…Of particular interest here are the number of stress conditions linked to disassembly of caveolae. While caveolae have been shown to protect cells against increased membrane tension, a remarkably extensive literature has linked caveolae to other stress conditions, including shear, UV, chemical, oxidative, heat, and gravitational stresses (Shi et al, 2015; Wang et al, 2015b; McMahon et al, 2019; Table 1 summarizes the widespread literature linking caveolae/caveolin to stress response/protection). Indirect evidence for an evolutionary conservation of this role is provided by analysis of the genome of the oyster Crassostrea gigas .…”

“…Our model proposes that caveolae, signaling proteins clustered on the PM outside of caveolae, and the lipids that make up the PM are in a “baseline/normal” state. However, upon exposure of the cell to an external stressor, such as an increase in membrane tension, caveolae are disassembled (Sinha et al, 2011); we hypothesize that this is a consequence of the release of the cavin coat complex and loss of the stability of the caveolar microdomain (McMahon et al, 2019; Sinha et al, 2011), which in turn releases the lipids enriched within the curved caveolar domain (Ariotti et al, 2014). Destabilization and release of caveolar lipids into the bulk membrane can indirectly affect protein clustering by modulation of the lipid nanoenvironment (as shown for PtdSer and Ras proteins) to modulate cellular signaling cascades (Ariotti et al, 2014).…”