Poly C Binding Protein 1 (PCBP1) is an RNA-binding protein that binds and regulates translational activity of subsets of cellular mRNAs. Depletion of PCBP1 is implicated in various carcinomas, but the underlying mechanism in tumorigenesis remains elusive. We performed a transcriptome-wide screen to identify novel bounding mRNA of PCBP1. The bind regions between PCBP1 with target mRNA were investigated by using point mutation and luciferase assay. Cell proliferation, cell cycle, tumorigenesis and cell apoptosis were also evaluated in ovary and colon cancer cell lines. The mechanism that PCBP1 affects p27 was analyzed by mRNA stability and ribosome profiling assays. We analyzed PCBP1 and p27 expression in ovary, colon and renal tumor samples and adjacent non-tumor tissues using RT-PCR, Western Blotting and immunohistochemistry. The prognostic significance of PCBP1 and p27 also analyzed using online databases. We identified cell cycle inhibitor p27Kip1 (p27) as a novel PCBP1-bound transcript. We then demonstrated that binding of PCBP1 to p27 3’UTR via its KH1 domain mainly stabilizes p27 mRNA, while enhances its translation to fuel p27 expression, prior to p27 protein degradation. The upregulated p27 consequently inhibits cell proliferation, cell cycle progression and tumorigenesis, whereas promotes cell apoptosis under paclitaxel treatment. Conversely, knockdown of PCBP1 in turn compromises p27 mRNA stability, leading to lower p27 level and tumorigenesis in vivo. Moreover, forced depletion of p27 counteracts the tumor suppressive ability of PCBP1 in the same PCBP1 over-expressing cells. Physiologically, we showed that decreases of both p27 mRNA and its protein expressions are well correlated to PCBP1 depletion in ovary, colon and renal tumor samples, independent of the p27 ubiquitin ligase Skp2 level. Correlation of PCBP1 with p27 is also found in the tamoxifen, doxorubincin and lapatinib resistant breast cancer cells of GEO database. Our results thereby indicate that loss of PCBP1 expression firstly attenuates p27 expression at post-transcriptional level, and subsequently promotes carcinogenesis. PCBP1 could be used as a diagnostic marker to cancer patients.

Acquired chemotherapy resistance is one of the main culprits in the relapse of breast cancer. But the underlying mechanism of chemotherapy resistance remains elusive. Here, we demonstrate that a small adaptor protein, SH3BGRL, is not only elevated in the majority of breast cancer patients but also has relevance with the relapse and poor prognosis of breast cancer patients. Functionally, SH3BGRL upregulation enhances the chemoresistance of breast cancer cells to the first-line doxorubicin treatment through macroautophagic/autophagic protection. Mechanistically, SH3BGRL can unexpectedly bind to ribosomal subunits to enhance PIK3C3 translation efficiency and sustain ATG12 stability. Therefore, inhibition of autophagy or silence of PIK3C3 or ATG12 can effectively block the driving effect of SH3BGRL on doxorubicin resistance of breast cancer cells in vitro and in vivo. We also validate that SH3BGRL expression is positively correlated with that of PIK3C3 or ATG12, as well as the constitutive occurrence of autophagy in clinical breast cancer tissues. Taken together, our data reveal that SH3BGRL upregulation would be a key driver to the acquired chemotherapy resistance through autophagy enhancement in breast cancer while targeting SH3BGRL could be a potential therapeutic strategy against breast cancer. Abbreviations: ABCs: ATP-binding cassette transporters; Act D: actinomycin D; ACTB/β-actin: actin beta; ATG: autophagy-related; Baf A₁: bafilomycin A₁; CASP3: caspase 3; CHX: cycloheximide; CQ: chloroquine; Dox: doxorubicin; FBS: fetal bovine serum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GEO: gene expression omnibus; GFP: green fluorescent protein; G6PD: glucose-6-phosphate dehydrogenase; GSEA: gene set enrichment analysis; IHC: immunochemistry; KEGG: Kyoto Encyclopedia of Genes and Genomes; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; 3-MA: 3-methyladenine; mRNA: messenger RNA; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; SH3BGRL: SH3 domain binding glutamate-rich protein-like; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1

Background/Aims: Three rare MAPK7 variants that predispose individuals to adolescent idiopathic scoliosis have previously been identified. However, the mechanism underlying the effects of the mutations remain unknown. Methods: Human mesenchymal stem cells (hMSCs) were isolated from both patients and healthy volunteer donors, and MAPK7 expression was detected by western blotting and real-time quantitative PCR (RT-qPCR). Zebrafish embryos were injected with mapk7 morpholinos or co-injected with morpholinos and wild-type (WT) MAPK7 messenger RNA (mRNA) at the one-cell stage, followed by calcein staining to evaluate bone formation. hMSCs were transfected with MAPK7 small interfering RNAs and osteogenesis was induced for 14 days. Alizarin red staining was performed and osteoblast markers were detected by western blotting and RT-qPCR. Since RPS6KA3 is a downstream target of MAPK7 and plays an important role in the osteogenesis, zebrafish embryos were then injected with rps6ka3 morpholinos, or co-injected with rps6ka3 or mapk7 morpholinos and WT RPS6KA3 mRNA at the one-cell stage. Results: MAPK7 expression in the patient group was much lower than in the control group. Morpholino-induced mapk7 knockdown in zebrafish embryos led to body curvature, which was significantly reversed by WT MAPK7 mRNA. Calcein staining revealed that mapk7-knockdown delayed the ossification of the vertebrae. MAPK7 silencing in hMSCs impaired osteogenesis and downregulated osteoblast marker expression. Morpholino-induced rps6ka3-knockdown in zebrafish embryos led to body curvature, which was reversed by WT RPS6KA3 mRNA. Interestingly, RPS6KA3 mRNA also partially reversed the phenotype induced by mapk7 morpholinos. Conclusion: Impaired osteogenesis is linked to mutant MAPK7-induced idiopathic scoliosis , and RPS6KA3 may play an important role in this process.