A Novel Golgi Retention Signal RPWS for Tumor Suppressor UBIAD1

Abstract

UBIAD1 plays critical roles in physiology including vitamin K and CoQ10 biosynthesis as well as pathophysiology including dyslipimedia-induced SCD (Schnyder’s corneal dystrophy), Parkinson’s disease, cardiovascular disease and bladder carcinoma. Since the subcellular localization of UBIAD1 varies in different cell types, characterization of the exact subcellular localization of UBIAD1 in specific human disease is vital for understanding its molecular mechanism. As UBIAD1 suppresses bladder carcinoma, we studied its subcellular localization in human bladder carcinoma cell line T24. Since fluorescent images of UBIAD1-EGFP in T24, human prostate cancer cell line PC-3, human embryonic kidney cell line HEK293 and human hepatocyte cell line L02 are similar, these four cell lines were used for present study. Using a combination of fluorescent microscopy and immunohistochemistry, it was found that UBIAD1 localized on the Golgi and endoplasmic reticulum (ER), but not on the plasma membrane, of T24 and HEK293 cells. Using scanning electron microscopy and western blot analysis, we found that UBIAD1 is enriched in the Golgi fraction extracted from the L02 cells, verifying the Golgi localization of UBAID1. Site-directed mutagenesis showed that the RPWS motif, which forms an Arginine finger on the UBIAD1 N terminus, serves as the Golgi retention signal. With both cycloheximide and brefeldin A inhibition assays, it was shown that UBIAD1 may be transported from the endoplasmic reticulum (ER) to the Golgi by a COPII-mediated mechanism. Based upon flow cytometry analysis, it is shown that mutation of the RPWS motif reduced the UBIAD1-induced apoptosis of T24 cells, indicating that the proper Golgi localization of UBIAD1 influences its tumor suppressant activity. This study paves the way for further understanding the molecular mechanism of UBIAD1 in human diseases.

UBIAD1 expression is associated with cardiac hypertrophy in spontaneously hypertensive rats

“…Previous studies have suggested that UBIAD1 regulates apoptosis through multiple mechanisms. For instance, UBIAD1 was reported to promote apoptosis through mediating Golgi function in a number of human cancer cell lines (39), and another study indicated that UBIAD1 induces apoptosis in bladder tumor cells through regulating cellular cholesterol (40). Consistent with the above findings, the present study revealed that decreased UBIAD1 expression was accompanied by increased apoptosis in SHR hearts.…”

The prenyltransferase UBIAD1 is the target of geranylgeraniol in degradation of HMG CoA reductase

“…Consistent with a role in the ERAD of reductase, UBIAD1 has been localized to membranes of the ER ( Nakagawa et al, 2010 ; Nickerson et al, 2013 ). However, it should be noted that the prenyltransferase has also been localized to membranes of the mitochondria ( Nickerson et al, 2010 ) as well as the Golgi ( Mugoni et al, 2013 ; Wang et al, 2013 ). In the experiment shown in Figure 5C , we examined the subcellular localization of endogenous UBIAD1 in SV-589 cells grown in medium containing FCS (fetal calf serum).…”

Functional Characterization of the Vitamin K2 Biosynthetic Enzyme UBIAD1

“…One of the major forms of vitamin K in humans, MK-4, is produced by cleavage of the phytyl side chain from dietary PK to release MD in the intestine, followed by delivery of MD through the mesenteric lymphatic system and blood circulation to tissues where it is then converted to MK-4 by a prenyltransferase such as UbiA prenyltransferase domain-containing protein 1 (UBIAD1) with geranylgeranyl diphosphate (GGPP) [ 12 – 14 ]. Recently, it has been reported that UBIAD1 catalyses the non-mitochondrial synthesis of coenzyme Q10 (CoQ10) in zebrafish [ 15 ]. CoQ10 exists in several forms and can be found in microorganisms, plants and mammals.…”