Early biomarkers and effective therapeutic strategies are desperately needed to treat pancreatic ductal adenocarcinoma (PDAC), which has a dismal 5-year patient survival rate. Here, we report that the novel tyrosine kinase PEAK1 is upregulated in human malignancies, including human PDACs and pancreatic intraepithelial neoplasia (PanIN). Oncogenic KRas induced a PEAK1-dependent kinase amplification loop between Src, PEAK1, and ErbB2 to drive PDAC tumor growth and metastasis in vivo. Surprisingly, blockade of ErbB2 expression increased Src-dependent PEAK1 expression, PEAK1-dependent Src activation, and tumor growth in vivo, suggesting a mechanism for the observed resistance of patients with PDACs to therapeutic intervention. Importantly, PEAK1 inactivation sensitized PDAC cells to trastuzumab and gemcitabine therapy. Our findings, therefore, suggest that PEAK1 is a novel biomarker, critical signaling hub, and new therapeutic target in PDACs.

Deregulation of protein synthesis is a hallmark of cancer cell proliferation, survival, and metastatic progression. eIF5A1, and its highly related isoform eIF5A2, are translation initiation factors that have been implicated in a range of human malignancies, but how they control cancer development and disease progression is still poorly understood. Here, we investigated how eIF5A proteins regulate pancreatic ductal adenocarcinoma (PDAC) pathogenesis. eIF5A proteins are the only known proteins regulated by a distinct posttranslational modification termed hypusination, which is catalyzed by two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). The highly selective nature of the hypusine modification and its amenability to pharmacological inhibition make eIF5A proteins attractive therapeutic targets. We found that the expression and hypusination of eIF5A proteins are upregulated in human PDAC tissues and in premalignant pancreatic intraepithelial neoplasia (PanIN) tissues isolated from Pdx-1-Cre: LSL-KRASG12D mice. Knockdown of eIF5A proteins in PDAC cells inhibited their growth in vitro and orthotopic tumor growth in vivo, whereas amplification of eIF5A proteins increased PDAC cell growth and tumor formation in mice. Small molecule inhibitors of DHPS and DOHH both suppressed eIF5A hypusination, preventing PDAC cell growth. Interestingly, we found that eIF5A proteins regulate PDAC cell growth by modulating the expression of PEAK1, a non-receptor tyrosine kinase essential for PDAC cell growth and therapy resistance. Our findings suggest that eIF5A proteins utilize PEAK1 as a downstream effector to drive PDAC pathogenesis, and that pharmacological inhibition of the eIF5A-hypusine-PEAK1 axis may provide a novel therapeutic strategy to combat this deadly disease.

SummaryLittle is known about the extracellular signaling factors that govern mammary stem cell behavior. Here, we identify CRIPTO and its cell-surface receptor GRP78 as regulators of stem cell behavior in isolated fetal and adult mammary epithelial cells. We develop a CRIPTO antagonist that promotes differentiation and reduces self-renewal of mammary stem cell-enriched populations cultured ex vivo. By contrast, CRIPTO treatment maintains the stem cell phenotype in these cultures and yields colonies with enhanced mammary gland reconstitution capacity. Surface expression of GRP78 marks CRIPTO-responsive, stem cell-enriched fetal and adult mammary epithelial cells, and deletion of GRP78 from adult mammary epithelial cells blocks their mammary gland reconstitution potential. Together, these findings identify the CRIPTO/GRP78 pathway as a developmentally conserved regulator of fetal and adult mammary stem cell behavior ex vivo, with implications for the stem-like cells found in many cancers.

Background: Eukaryotic translation initiation factor 5A (eIF5A) regulates pancreatic cancer pathogenesis. Results: eIF5A was shown to control the expression of a set of key signaling molecules including RhoA and ROCK2, and to promote the invasive potential of pancreatic cancer cells. Conclusion: Hypusine/eIF5A/RhoA/ROCK cascade promotes pancreatic cancer cell metastasis. Significance: eIF5A may be a novel druggable target to treat metastatic pancreatic cancer.