RBEL1 Is a Novel Gene That Encodes a Nucleocytoplasmic Ras Superfamily GTP-binding Protein and Is Overexpressed in Breast Cancer

Abstract

Rab family proteins are generally known as regulators of protein transport and trafficking. A number of Rab proteins have been implicated in cancer development and/or progression. Here we report the identification of a novel Rab-like protein, which we have named RBEL1 (Rab-like protein 1) for its higher similarity to the Rab subfamily members. We have characterized two isoforms of RBEL1 including the predominant RBEL1A and the less abundant RBEL1B that results from alternative splicing. Both isoforms harbor conserved N-terminal guanine trinucleotide phosphate (GTP) binding domains and, accordingly, are capable of binding to GTP. Both isoforms contain variable C termini and exhibit differential subcellular localization patterns. Unlike known Rabs that are mostly cytosolic, RBEL1B predominantly resides in the nucleus, whereas RBEL1A is localized primarily to the cytosol. Interestingly, a point mutation affecting RBEL1B GTP binding also alters the ability of mutant protein to accumulate in the nucleus, suggesting GTP binding potential to be important for RBEL1B nuclear localization. Our results also indicate that RBEL1A is overexpressed in about 67% of primary breast tumors. Thus, RBEL1A and RBEL1B are novel Rab-like proteins that localize in the nucleus and cytosol and may play an important role in breast tumorigenesis.

CHCM1/CHCHD6, Novel Mitochondrial Protein Linked to Regulation of Mitofilin and Mitochondrial Cristae Morphology

“…Western Blotting, S-tag Pull-down, and ImmunoprecipitationWestern blotting and immunoprecipitations were done by standard procedures as we have described previously (25,26). S-tag pull-down experiments were performed using human cancer cells as well as bacterial lysates.…”

Negative regulation of p53 by Ras superfamily protein RBEL1A

“…RBEL1A protein is predominantly GTP bound and functions as a GTPase. RBEL1A was found to be overexpressed in big portion of primary breast (67%) and colon (47%) cancer samples when compared to matching normal tissues (Montalbano et al, 2007). Furthermore, RBEL1A knockdown triggered severe growth suppression, cell death and activation of caspase 3 in various cancer cell lines suggesting that the expression of RBEL1A appeared to be important for maintaining cell growth and survival .…”

“…1B left middle panel shows that RBEL1A protein expression was sufficiently depleted by the expression of lentiviral-mediated RBEL1A shRNA that was used in our previous studies ). And it is of note that our previous studies have shown that RBEL1A is a glycosylated protein (Montalbano et al, 2007;Montalbano et al, 2009) and it exhibits multiple band patterns ,100-110 kDa and 125-130 kDa on the western blotting depending on the degree of glycosylation of the protein. Importantly, we found that knockdown of RBEL1A in these cells led to increased p53 protein expression.…”

“…We have previously shown that RBEL1A is overexpressed in human primary breast (67%) and colon cancers (47%) and that RBEL1A suppression via shRNA knockdown triggers cell death and growth suppression in human cancer cells (Montalbano et al, 2007;Montalbano et al, 2009). To further study the function of RBEL1A and to investigate how elevated levels of RBEL1A would affect cellular functions, we examined the effect of exogenous RBEL1A on a number of tumor-related proteins; results presented in Fig.…”

“…We have recently reported the identification and characterization of a novel Rab-like GTP-binding protein named RBEL1A (Montalbano et al, 2007;Montalbano et al, 2009). RBEL1A protein harbors a N-terminal Ras/Rab-like GTPase domain followed by a GTP-binding regulatory domain, a proline-rich region and a C-terminal nuclear localization signal ).…”