Subcellular distribution and expression of prenylated Rab acceptor 1 domain family, member 2 (PRAF2) in malignant glioma: Influence on cell survival and migration

Abstract

Our previous studies revealed that the expression of the 19-kDa protein prenylated Rab acceptor 1 domain family, member 2 (PRAF2) is elevated in cancer tissues of the breast, colon, lung, and ovary, when compared to noncancerous tissues of paired samples. PRAF2 mRNA expression also correlated with several genetic and clinical features and is a candidate prognostic marker in the pediatric cancer neuroblastoma. The PRAF2-related proteins, PRAF1 and PRAF3, play multiple roles in cellular processes, including endo ⁄ exocytic vesicle trafficking and glutamate uptake. PRAF2 shares a high sequence homology with these family members, but its function remains unknown. In this study, we examined PRAF2 mRNA and protein expression in 20 different human cancer types using Affymetrix microarray and human tissue microarray (TMA) analyses, respectively. In addition, we investigated the subcellular distribution of PRAF2 by immunofluorescence microscopy and cell fractionation studies. PRAF2 mRNA and protein expression was elevated in several cancer tissues with highest levels in malignant glioma. At the molecular level, we detected native PRAF2 in small, vesicle-like structures throughout the cytoplasm as well as in and around cell nuclei of U-87 malignant glioma cells. We further found that monomeric and dimeric forms of PRAF2 are associated with different cell compartments, suggesting possible functional differences. Importantly, PRAF2 down-regulation by RNA interference significantly reduced the cell viability, migration, and invasiveness of U-87 cells. This study shows that PRAF2 expression is elevated in various tumors with exceptionally high expression in malignant gliomas, and PRAF2 therefore presents a candidate molecular target for therapeutic intervention. (Cancer Sci 2010; 101: 1624-1631 M alignant glioma (MG) is the most common adult brain tumor and is as yet almost incurable. Due to its invasive nature and resistance to chemotherapy, the median survival is only 14.6 months, even with the most advanced care.(1) Therefore, there is an urgent need for new diagnostic markers and potential drug targets. Proteins which are over-expressed in malignant tissues but not in the healthy tissue of origin, can provide important insights into understanding the underlying molecular mechanisms of malignant transformation, and also represent good candidate targets for drug development and intervention.The prenylated Rab acceptor 1 domain family (PRAF) proteins have recently gained increasing attention in the study of cancer. In humans, three PRAF members exist (PRAF1-3), all of which have four transmembrane domains, a hydrophilic N-and C-terminus, and a prenylated Rab acceptor (PRA) motif. PRAF1 and PRAF3 were shown to interact with membraneorganizing Rab GTPases.(2-5) In addition, they bind with proteins that regulate several well-known cancer signaling pathways. For example, PRAF1 binds to and blocks the nuclear transport of b-catenin (6) and interacts with Ras and Rho GTPases, (7) associated with the promotion of metastasis. PRAF1 ...

PRAF3 induces apoptosis and inhibits migration and invasion in human esophageal squamous cell carcinoma

“…In recent years, PRAF3 has gained increasing attention in tumor research. Unlike other members (PRAF1 and PRAF2) of the PRA family which promote tumor cell proliferation and migration and hence may function as oncogenes [11-13], PRAF3 is considered as a tumor suppressor since it could induce cell apoptosis and inhibit metastasis in tumors such as breast cancer, cervical cancer, melanoma and osteosarcoma [7,9,10]. However, the biological role of PRAF3 in ESCC has not been documented.…”

An Arabidopsis Prenylated Rab Acceptor 1 Isoform, AtPRA1.B6, Displays Differential Inhibitory Effects on Anterograde Trafficking of Proteins at the Endoplasmic Reticulum

“…PRA2 belongs to the Yip6 subfamily and localizes to the ER (Abdul-Ghani et al, 2001;Pfeffer and Aivazian, 2004). PRA2/PRA2F expression levels are elevated in various cancer cells, and the encoded proteins are enriched in synaptic vesicles in neuronal cells (Koomoa et al, 2008;Borsics et al, 2010). In neuronal cells, Yip6b and JM4, also members of the Yip6 subfamily, are involved in regulating the ER exit of the neuron-specific Na + /K + Glu transporter EAAC1 as well as selected neurotransmitter transporters (Ruggiero et al, 2008).…”

GABAB receptor cell-surface export is controlled by an endoplasmic reticulum gatekeeper

“…GB1 staining (Supplementary Figure S3a for GB1 antibody specificity) overlapped with both ER (KDEL receptor) and Golgi (GM130) markers, whereas PRAF2 was mainly colocalized with the ER marker (76.7 ± 6.7%, Figure 1d), consistent with previous studies. 42 PRAF2 controls GB1 export and regulates GABA B function at the cell surface of neurons Based on the experiments above, GB1 and PRAF2 likely interact in the ER, where GB1 is retained in the absence of heterodimerization with GB2. To investigate whether PRAF2 could control the exit of GB1 from the ER, hippocampal neurons were transfected with siRNAs to downmodulate PRAF2 expression.…”

“…Consistent with this hypothesis, a two-to threefold increase of PRAF2 mRNA was reported in human brain tumors compared with normal samples. 36,42 In conclusion, we have uncovered a mechanism by which GPCR function can be regulated by the competing effects exerted by gatekeepers and escorts on receptor trafficking to the cell surface. Although interfering with this process causes major pathological effects in mice models, further studies are necessary to appreciate whether deregulation of gatekeeper and/or escort expression levels are pathogenic in human diseases.…”

“…38,39 PRAF2 identified in a yeast two-hybrid screen as an interacting partner of the chemokine receptor CCR5 40 was found enriched in human brain 41 and overexpressed in multiple cancers. 36,42 However, no specific biological function has so far been attributed to PRAF2.…”