Reggie-1 and reggie-2 localize in non-caveolar rafts in epithelial cells: cellular localization is not dependent on the expression of caveolin proteins.
ABSTRACT Reggie-1 and reggie-2 are highly conserved and widely expressed proteins associated with membrane rafts. The molecular function of reggies remains to be clarified, but recent data indicate that they are involved in various cellular processes such as insulin signaling, phagocytosis and actin remodeling. However, there is discrepancy in the literature if reggies are associated with caveolae or non-caveolar rafts. Reggies are expressed and raft associated also in many cells which do not contain caveolae, such as neurons and lymphocytes. However, it is not clear if the function or localization of reggies are dependent on the presence of caveolae and expression of caveolin-1 protein. In this study, we directly addressed this question in epithelial cells. We could show that ectopic expression of caveolin-1 does not result in any change in the cellular localization of reggie-1, which is present at the plasma membrane also in the absence of caveolin-1. On the other hand, caveolin-2, which localizes in caveolae, is dependent on caveolin-1 expression in order to be localized at the plasma membrane. Although reggie-1 and reggie-2 strongly interact with each other, we did not detect a direct interaction between caveolin-1 and reggies by means of a yeast two-hybrid assay, nor could reggies be co-immunoprecipitated with caveolin-1. Furthermore, endogenous reggie-1 and -2 were found not to colocalize with caveolin-1 in epithelial cells. Thus, our data indicate that reggies are localized in microdomains different from caveolae, and the function of reggies is different from and independent of caveolin-1.
[Show abstract] [Hide abstract]
ABSTRACT: Flotillin 1 and 2 are ubiquitous and highly conserved proteins. They were initially discovered in 1997 as being associated with specific caveolin-independent cholesterol- and glycosphingolipid-enriched membrane microdomains and as being expressed during axon regeneration. Flotillins have a role in a large number of physiopathological processes, mainly through their function in membrane receptor clustering and in the regulation of clathrin-independent endocytosis. In this Commentary, we summarize the research performed so far on the role of flotillins in cell-cell adhesion. Recent studies have demonstrated that flotillins directly regulate the formation of cadherin complexes. Indeed, flotillin microdomains are required for the dynamic association and stabilization of cadherins at cell-cell junctions and also for cadherin signaling. Moreover, because flotillins regulate endocytosis and also the actin cytoskeleton, they could have an indirect role in the assembly and stabilization of cadherin complexes. Because it has also recently been shown that flotillins are overexpressed during neurodegenerative diseases and in human cancers, where their upregulation is associated with metastasis formation and poor prognosis, understanding to what extent flotillin upregulation participates in the development of such pathologies is thus of particular interest, as well as how, at the molecular level, it might affect cell adhesion processes.Journal of Cell Science 11/2014; DOI:10.1242/jcs.159764 · 5.33 Impact Factor
Protein Phosphorylation in Human Health, Edited by Cai Huang, 01/2012: chapter 10; Intech Open Science., ISBN: ISBN 978-953-51-0737-8
[Show abstract] [Hide abstract]
ABSTRACT: To investigate the expression and clinical significance of flotillin-2 (FLOT2) in cervical cancer (CC). We examined FLOT2 mRNA levels in 10 pairs of cervical cancer and adjacent normal tissues. Immunohistochemistry was performed to analyze FLOT2 protein expression in 115 archived cervical cancer samples. The association between FLOT2 levels, clinicopathologic factors and prognosis was analyzed statistically as well. The cancer tissues of CC patients had clearly increased expression of FLOT2 at mRNA level as compared to adjacent nontumorous tissues. Survival analysis of CC patients indicated that FLOT2 expression was significantly associated with poor overall and local recurrence-free survival (P = 0.025 and P = 0.028, respectively). Moreover, FLOT2 expression was significantly correlated with clinical stage, tumor differentiation, and lymph nodes metastasis. Multivariate analysis revealed that FLOT2 expression was an independent prognostic factor for overall survival in CC patients. FLOT2 may serve as an oncogene in the development of CC, and may serve as a clinicopathologic biomarker for prognosis in CC patients.