Rlip Depletion Alters Oncogene Transcription at Multiple Distinct Regulatory Levels.

Ashly Hindle,Jihyun Lee,Sharda P Singh,Christopher J Peterson,Philip T Palade,Sanjay Awasthi,P Hemachandra Reddy,Chhanda Bose

doi:10.3390/cancers14030527

Abstract

Rlip76 (Rlip) is a multifunctional membrane protein that facilitates the high metabolic rates of cancer cells through the efflux of toxic metabolites and other functions. Rlip inhibition or depletion results in broad-spectrum anti-cancer effects in vitro and in vivo. Rlip depletion effectively suppresses malignancy and causes global reversion of characteristic CpG island methylomic and transcriptomic aberrations in the p53-null mouse model of spontaneous carcinogenesis through incompletely defined signaling and transcriptomic mechanisms. The methylome and transcriptome are normally regulated by the concerted actions of several mechanisms that include chromatin remodeling, promoter methylation, transcription factor interactions, and miRNAs. The present studies investigated the interaction of Rlip depletion or inhibition with the promoter methylation and transcription of selected cancer-related genes identified as being affected by Rlip depletion in our previous studies. We constructed novel promoter CpG island/luciferase reporter plasmids that respond only to CpG methylation and transcription factors. We found that Rlip depletion regulated expression by a transcription factor-based mechanism that functioned independently of promoter CpG methylation, lipid peroxidation, and p53 status.

Highlights

Rlip76 (Rlip, the 76 kDa isoform encoded by the RALBP1 gene at human genomic locus 18p11.22) has been well-established by several lines of evidence as a permissivity factor required for oncogenic transformation, cancer growth, and invasion/metastasis [1–7]
The degree of transcriptional regulation exerted by Rlip knockdown significantly correlated (p < 0.05) with the degree of Rlip depletion for PRKCA, CREBBP, and PPARA (Figure 1C)
MAPK14 and PRKCZ showed non-significant positive relationships between the degree of Rlip depletion and degree of expression change. These results support a causal relationship between Rlip depletion and transcriptional regulation

Summary

Introduction

Rlip (Rlip, the 76 kDa isoform encoded by the RALBP1 gene at human genomic locus 18p11.22) has been well-established by several lines of evidence as a permissivity factor required for oncogenic transformation, cancer growth, and invasion/metastasis [1–7]. Rlip depletion or inhibition inhibits the growth of breast, lung, colon, kidney, and prostate cancer as well as neuroblastoma in xenografts using immune-deficient mouse models and in syngeneic melanoma implants in immune-sufficient mice [12–19]. It is not currently known which of the many aspects of Rlip physiology are causal with respect to the remarkable broad-spectrum anticancer activity seen with Rlip depletion or inhibition. It has become clear that Rlip inhibition results in global methylomic and transcriptomic changes, affecting many pathways, including several cancer-related pathways [1] These methylomic changes included both methylation and demethylation events at both promoter CpG islands and gene body CpG dinucleotides

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Discussion

Conclusion