Journal of Biological Chemistry
Volume 274, Issue 18, 30 April 1999, Pages 12702-12709
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CELL BIOLOGY AND METABOLISM
Flotillins/Cavatellins Are Differentially Expressed in Cells and Tissues and Form a Hetero-oligomeric Complex with Caveolins in Vivo: CHARACTERIZATION AND EPITOPE-MAPPING OF A NOVEL FLOTILLIN-1 MONOCLONAL ANTIBODY PROBE*

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Caveolae are vesicular organelles that represent a subcompartment of the plasma membrane. Caveolins and flotillins are two families of mammalian caveolae-associated integral membrane proteins. However, it remains unknown whether flotillins interact with caveolin proteins to form a stable caveolar complex or if expression of flotillins can drive vesicle formation. Here, we examine the cell type and tissue-specific expression of the flotillin gene family. For this purpose, we generated a novel monoclonal antibody probe that recognizes only flotillin-1. A survey of cell and tissue types demonstrates that flotillins 1 and 2 have a complementary tissue distribution. At the cellular level, flotillin-2 was ubiquitously expressed, whereas flotillin-1 was most abundant in A498 kidney cells, muscle cell lines, and fibroblasts. Using three different models of cellular differentiation, we next examined the expression of flotillins 1 and 2. Taken together, our data suggest that the expression levels of flotillins 1 and 2 are independently regulated and does not strictly correlate with known expression patterns of caveolin family members. However, when caveolins and flotillins are co-expressed within the same cell, as in A498 cells, they form a stable hetero-oligomeric “caveolar complex.” In support of these observations, we show that heterologous expression of murine flotillin-1 in Sf21 insect cells using baculovirus-based vectors is sufficient to drive the formation of caveolae-like vesicles. These results suggest that flotillins may participate functionally in the formation of caveolae or caveolae-like vesicles in vivo. Thus, flotillin-1 represents a new integral membrane protein marker for the slightly larger caveolae-related domains (50–200 nm) that are observed in cell types that fail to express caveolin-1. As a consequence of these findings, we propose the term “cavatellins” be used (instead of flotillins) to describe this gene family.

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*

This work was supported by a National Institutes of Health Grant (NCI) R01-CA-80250 (to M. P. L.) and grants from the Charles E. Culpeper Foundation (to M. P. L.), G. Harold and Leila Y. Mathers Charitable Foundation (to M. P. L.), and the Sidney Kimmel Foundation for Cancer Research (to M. P. L.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Recipient of National Institutes of Health (NCI) post-doctoral fellowship CA-71326.

Present address: Allergan, Inc., 2525 Dupont Dr., Irvine, CA 92713.

Supported by National Institutes of Health FIRST Award MH-56036 (to T. O.).