Abstract
The prostate cancer antigen gene 3 (PCA3) is embedded in an intron of a second gene BMCC1 (Bcl2-/adenovirus E1B nineteen kDa-interacting protein 2 (BNIP-2) and Cdc42GAP homology BCH motif-containing molecule at the carboxyl terminal region 1) which is also upregulated in prostate cancer. BMCC1 was initially annotated as two genes (C9orf65/PRUNE and BNIPXL) on either side of PCA3 but our data suggest that it represents a single gene coding for a high molecular weight protein. Here we demonstrate for the first time the expression of a >300 kDa BMCC1 protein (BMCC1-1) in prostate cancer and melanoma cell lines. This protein was found exclusively in the microsomal fraction and localised to cytoplasmic vesicles. We also observed expression of BMCC1 protein in prostate cancer sections using immunohistology. GST pull down, immunoprecipitation and mass spectrometry protein interaction studies identified multiple members of the Adaptor Related Complex 2 (AP-2) as BMCC1 interactors. Consistent with a role for BMCC1 as an AP-2 interacting endosomal protein, BMCC1 co-localised with β-adaptin at the perinuclear region of the cell. BMCC1 also showed partial co-localisation with the early endosome small GTP-ase Rab-5 as well as strong co-localisation with internalised pulse-chase labelled transferrin (Tf), providing evidence that BMCC1 is localised to functional endocytic vesicles. BMCC1 knockdown did not affect Tf uptake and AP-2 knockdown did not disperse BMCC1 vesicular distribution, excluding an essential role for BMCC1 in canonical AP-2 mediated endocytic uptake. Instead, we posit a novel role for BMCC1 in post-endocytic trafficking. This study provides fundamental characterisation of the BMCC1 complex in prostate cancer cells and for the first time implicates it in vesicle trafficking.
Highlights
Prostate cancer is a commonly diagnosed malignancy and a leading cause of cancer deaths worldwide
BMCC1-1 protein is expressed in select cancers hBMCC1 is a large and complex transcriptional unit, with the routinely used prostate cancer biomarker hPCA3 embedded in BMCC1 intron 6
We have previously shown that the prostate cancer cell line LNCaP expresses high levels of both BMCC1-1 and prostate cancer antigen gene 3 (PCA3) RNAs [5]
Summary
Prostate cancer is a commonly diagnosed malignancy and a leading cause of cancer deaths worldwide. This condition exhibits a wide spectrum of histological changes and behaviours, ranging from premalignant lesions, to localized prostate cancers that follow an indolent course to a percentage of cancers that metastasize early and progress rapidly [1]. One of the most promising biomarkers for prostate cancer is the non-coding RNA PCA3 [2,3] This RNA was identified as a prostate cancer biomarker by differential display analysis of RNAs from histologically normal and malignant tissue from the same patients, and was originally described as Differential Display clone 3 (DD3) [2]. High levels of PCA3 expression are strongly associated with malignant transformation of the prostate epithelium, the biological basis for this correlation has not been elucidated [2,3,4]
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