Heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is a RNA binding protein that plays important role in the biogenesis of mRNA, such as alternative splicing and mRNA stability. We have previously demonstrated that hnRNP A1 has diminished protein levels and shows cytoplasmic accumulation in senescent human diploid fibroblasts. Recent reports showed that p38 MAP kinase (p38 MAPK), a member of the MAP kinase family is necessary and sufficient for the cytoplasmic accumulation of hnRNP A1 by stress stimuli such as osmotic shock. p38 MAP kinase has been shown to be involved in cell proliferation and the induction of senescence in response to extracellular stimuli. However, the relationship between hnRNP A1 and p38 MAPK and the roles of hnRNP A1 in cellular senescence have not yet been elucidated. Here we show that hnRNP A1 forms a complex with phospho-p38 MAPK in vivo. Inhibition of p38 MAPK activity with SB203580 elevated hnRNP A1 protein levels and prohibited the cytoplasmic accumulation of the protein, but not hnRNP A2, in senescent cells. The phosphorylation level of hnRNP A1 was elevated in senescent cells. Reduction of hnRNP A1 and A2 levels by siRNA transfection induced a senescence-like morphology and elevated the level of F-actin, a marker of senescence. These results suggest that the expression levels and subcellular distribution of hnRNP A1 are regulated in a p38 MAPK-dependent manner, probably via its phosphorylation. Our results also suggest that hnRNP A2 in addition to hnRNP A1 may play a role in establishing the senescence phenotype.

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Highlights Mechanotransduction through cell surface GAGs is a potential driver of metastasis. SAHA, a histone deacetylase inhibitor, reduces tumor cell NDST1 and HS. SAHA blocked metastasis of highly metastatic renal carcinoma cells in a mouse model. Reduction of hyaluronic acid suppresses metastasis in a mouse kidney cancer model.

The surface proteoglycan/glycoprotein layer (glycocalyx) on tumor cells has been associated with cellular functions that can potentially enable invasion and metastasis. In addition, aggressive renal carcinoma cells (SN12L1) with high metastatic potential have enhanced invasion rates compared to low metastatic (SN12C) cells in response to interstitial flow stimuli in vitro. Our previous studies suggest that heparan sulfate (HS) and hyaluronic acid (HA) in the glycocalyx play an important role in this flow mediated mechanotransduction and upregulation of invasive and metastatic potential. In our recent study, SN12L1 cells were genetically modified to suppress HS production by knocking down its synthetic enzyme NDST1. Using modified Boyden chambers with defined interstitial flow, we showed that flow‐enhanced invasion is suppressed in HS deficient cells. We also examined two prominent HSPGs on renal carcinoma cells – glypican‐1 and syndecan‐1 and one prominent HA receptor – CD44. We observed higher glypican‐1 levels in flow dependent SN12L1 cells when compared to SN12C cells. Caki‐1 (highly metastatic) cells did not display flow‐dependent invasion in vitro and did not display elevated glypican‐1 compared to low metastatic Caki‐2 cells. However we did observe significantly increased HS, HA, syndecan‐1 and CD44 in Caki‐1 compared to Caki‐2 cells suggesting an alternative mechanism for reported higher metastatic rates in these cells. All of our data are consistent with the hypothesis that glypican‐1 is the core protein responsible for flow sensing in metastatic cancer cells. This is also consistent with observations in endothelial cells. To assess the ability of tumor cells to metastasize in vivo, parental or HS knockdown SN12L1 cells expressing fluorescent reporters were injected into kidney capsules in SCID mice. Histological analysis confirmed that there was a large reduction (95%) in metastasis to distant organs by tumors formed from knockdown cells compared to control cells with intact HS. The reduction was even greater (98%) in lungs where most of the metastases from the control cells were observed. The ability of these knockdown cells to invade surrounding tissue was also impaired. The substantial inhibition of metastasis and invasion upon reduction of HS suggests an active role for the tumor cell glycocalyx and glypican‐1 in tumor progression.Support or Funding InformationGrant: RO1CA204949 Targeting glycocalyx mediated mechanisms of tumor metastsisThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.