Transcriptome-Wide Effects of Sphingosine Kinases Knockdown in Metastatic Prostate and Breast Cancer Cells: Implications for Therapeutic Targeting

Abstract

Sphingosine kinases 1 and 2 (SK1 and SK2) are proto-oncogenic isozymes expressed in many human tumors and associated with chemoresistance and poor prognosis. They are well-recognized therapy targets and their inhibition was shown to induce tumor volume reduction and chemosensitization in multiple cancer models. Oncogenic signaling is extremely complex and often cross-regulated. Designing molecular therapies and their combinations requires rational approaches to avoid redundant targeting or developing resistance. In this study, we have performed RNA transcriptome microarray analysis of two breast and two prostate metastatic cancer cell lines treated with siRNAs targeting SK1 or SK2. In prostate cancer cell lines SK1 knockdown (KD) has significantly changed expression of several genes including downregulation of NSUN2, G3BP2 and upregulation of ETS1. SK2 KD also affected expression of multiple genes including downregulation of CAPZA1 NSUN3 and ADPGK and upregulation of VDAC1, IBTK, ETS1 , and MKNK2 . Similarly, in breast cancer cells SK1 KD led to downregulation of NSUN2, NFATC3, CDK2 , and G3BP2 and upregulation of GTF2B, TTC17 , and RAB23 . SK2 KD in breast cancer cells has decreased expression of ITGAV and CAPZA1 and increased expression of GTF2B and ST13 . Gene-set enrichment analysis of known biochemical pathways showed that in prostate and breast cell lines SKs KD have altered multiple pathways. SK1 KD altered chromatin assembly, regulation of G1/S transition and mitosis, Wnt and MAP kinase signaling and cell motility. SK2 KD altered RAS protein signal transduction, regulation of MAP kinase and serine/threonine kinase activity, cell motility, small GTPase mediated signal transduction and phosphatidylinositol 3-kinase (PI3K) signaling. Through genome-wide microarray analysis, we have identified important molecular pathways affected by SK1 and SK2 KD. It appears that while KD of both genes leads to a decrease in individual pro-tumorigenic genes, there is a universal cellular response resulting in upregulation of several known pro-survival and pro-tumorigenic pathways such as MAPK, RAS, and PI3K, which may mediate cancer resistance to anti-SKs therapies. Our data point out to the potential advantage of certain molecular therapy combinations in targeting prostate and breast cancer. Further signaling studies are required to confirm the individual involvement of identified pathways.

The RNA Methyltransferase NSUN2 and Its Potential Roles in Cancer

“…Sphingosine kinases have been shown to be potential targets for therapy in breast cancer [ 121 , 122 ]. In this regard, knockdown of Sphingosine kinase 1 (SK1) was associated with downregulation of NSUN2 in breast and prostate cancer cells [ 123 ], suggesting that pharmacological inhibitors of SK1 could potentially benefit cancers with overexpressed NSUN2 [ 124 ]. At the same time, directly knocking down NSUN2 in HeLa cells has been shown to potentiate the sensitivity of the cells to 5-fluorouracil (5-FU) but not that of cisplatin or paclitaxel [ 125 ].…”

Ras and Wnt Interaction Contribute in Prostate Cancer Bone Metastasis

“…Chen et al illustrated that miR-34a acts as a tumor suppressor in PCa through downregulating both TCF7 and BIRC5, which are Wnt and Ras signaling effectors, respectively [159], suggesting an interplay between WNT signaling and miR-34a expression in Ras-activated PCa. Other upstream regulators, like sphingosine kinase 1/2 (SK1/2) [160], the TMPRSS2:ERG fusion mutation [161], and ss5TMD4 [162], were demonstrated to modulate both Wnt and Ras signaling. In conclusion, these aforementioned studies emphasized the tight crosstalk between Ras and Wnt signaling in PCa metastasis and point to expected Ras/Wnt co-regulators that have been proven in other cancers.…”

The Importance of Sphingosine Kinase in Breast Cancer: A Potential for Breast Cancer Management

“…Once exported, S1P acts on S1PR3, which stimulates ERK1/2 of the RAS/RAF/MEK/ERK signal transduction pathway leading to cancer cell proliferation [ 31 ]. S1P and S1PR3 may also stimulate AKT of the PI3K/AKT/mTOR signaling pathway producing a similar effect [ 15 ]. Simultaneously, the E2-ERα complex reaches the nucleus increasing certain transcription factors, and, in turn, promotes breast cancer cell growth.…”