Degradation of proteins that are retained in the quality control apparatus of the endoplasmic reticulum (ER) has been attributed to a third proteolytic system, distinct from the lysosomal and the cytoplasmic ubiquitindependent proteosomal proteolytic pathways. However, several recent studies have shown that ER degradation of a mutant membrane protein, CFTR⌬F508, is at least in part mediated from the cytoplasmic side by the 26 S proteasome. In this study, we examined the possibility that ER degradation of mutant secretory protein ␣ 1 -antitrypsin (␣ 1 -AT) Z, the mutant protein associated with infantile liver disease and adult-onset emphysema of ␣ 1 -AT deficiency, is mediated by the proteasome. The results show that a specific proteasome inhibitor, lactacystin, inhibits ER degradation of ␣1-ATZ in transfected human fibroblast cell lines and in a cell-free microsomal translocation system. Although it is relatively easy to conceptualize how a transmembrane protein like CFTR⌬F508 might be accessible on the cytoplasmic aspect of the ER membrane for ubiquitination and degradation by the proteasome, it is more difficult to conceptualize how this might occur for a luminal polypeptide. The results show that, once within the lumen of the ER, ␣ 1 -ATZ interacts with the transmembrane molecular chaperone calnexin and specifically induces the polyubiquitination of calnexin. The results, therefore, provide evidence that the proteasome, from its cytoplasmic localization, induces the degradation of the luminal ␣ 1 -ATZ molecule by first attacking the cytoplasmic tail of calnexin molecules that are associated with ␣ 1 -ATZ.

The endothelial cell protein C receptor (EPCR) shares ϳ20% sequence identity with the major histocompatibility complex class 1/CD1 family of molecules, accelerates the thrombin-thrombomodulin-dependent generation of activated protein C, a natural anticoagulant, binds to activated neutrophils, and can undergo translocation from the plasma membrane to the nucleus. Blocking protein C/activated protein C binding to the receptor inhibits not only protein C activation but the ability of the host to respond appropriately to bacterial challenge, exacerbating both the coagulant and inflammatory responses. To understand how EPCR accomplishes these multiple tasks, we solved the crystal structure of EPCR alone and in complex with the phospholipid binding domain of protein C. The structures were strikingly similar to CD1d. A tightly bound phospholipid resides in the groove typically involved in antigen presentation. The protein C binding site is outside this conserved groove and is distal from the membrane-spanning domain. Extraction of the lipid resulted in loss of protein C binding, which could be restored by lipid reconstitution. CD1d augments the immune response by presenting glycolipid antigens. The EPCR structure is a model for how CD1d binds lipids and further suggests additional potential functions for EPCR in immune regulation, possibly including the anti-phospholipid syndrome.

Previous studies observed that there is about 100 ng/ml soluble endothelial cell protein C receptor (EPCR) in human plasma and that the levels increase in inflammatory diseases. In this study we examine the potential mechanisms involved in release of EPCR from cells. We find that EPCR is released from the surface of endothelium and transfected 293 cells by a metalloprotease in a constitutive fashion. The mass of soluble EPCR is 4 kDa less than intact EPCR. Release is blocked by either the hydroxamic acid based inhibitor, KD-IX-73-4 or by 1,10-phenanthroline, but not by matrix metalloprotease inhibitors. Release is stimulated by phorbol 12-myristate 13-acetate, thrombin, interleukin-1␤, and hydrogen peroxide. Stimulation with these agents reduces EPCR expression levels sufficiently to decrease the rate of protein C activation to a limited extent. The influence of phorbol 12-myristate 13-acetate on both EPCR release and inhibition of protein C activation are enhanced by microtubule disruption with nocodazole. EPCR release is augmented by transfection of EPCR expressing 293 cells with caveolin, suggesting that release is caveolae dependent. These studies indicate that metalloproteolytic release of EPCR is a highly regulated process that is sensitive to both coagulation factors and inflammatory mediators.

Stem cell pluripotency, angiogenesis and epithelial-mesenchymal transition (EMT) have been shown to be significantly upregulated in pancreatic ductal adenocarcinoma (PDAC) and many other aggressive cancers. The dysregulation of these processes is believed to play key roles in tumor initiation, progression, and metastasis, and is contributory to PDAC being the fourth leading cause of cancer-related deaths in the US. The tumor suppressor miRNA miR-145 downregulates critical pluripotency factors and oncogenes and results in repressed metastatic potential in PDAC. Additionally, the miR-200 family regulates several angiogenic factors which have been linked to metastasis in many solid tumors. We have previously demonstrated that downregulation of DCLK1 can upregulate critical miRNAs in both in vitro and in vivo cancer models and results in downregulation of c-MYC, KRAS, NOTCH1 and EMT-related transcription factors. A recent report has also shown that Dclk1 can distinguish between normal and tumor stem cells in Apc min/+ mice and that ablation of Dclk1+ cells resulted in regression of intestinal polyps without affecting homeostasis. Here we demonstrate that the knockdown of DCLK1 using poly(lactide-co-glycolide)-encapsulated-DCLK1-siRNA results in AsPC1 tumor growth arrest. Examination of xenograft tumors revealed, (a) increased miR-145 which results in decreased pluripotency maintenance factors OCT4, SOX2, NANOG, KLF4 as well as KRAS and RREB1; (b) increased let-7a which results in decreased pluripotency factor LIN28B; and (c) increased miR-200 which results in decreased VEGFR1, VEGFR2 and EMT-related transcription factors ZEB1, ZEB2, SNAIL and SLUG. Specificity of DCLK1 post-transcriptional regulation of the downstream targets of miR-145, miR-200 and let-7a was accomplished utilizing a luciferase-based reporter assay. We conclude that DCLK1 plays a significant master regulatory role in pancreatic tumorigenesis through the regulation of multiple tumor suppressor miRNAs and their downstream pro-tumorigenic pathways. This novel concept of targeting DCLK1 alone has several advantages over targeting single pathway or miRNA-based therapies for PDAC.

Renal clear cell carcinoma (RCC) is the most common type of kidney cancer and the 8th most common cancer overall in the US. RCC survival rates drop precipitously with regional and distant spread and recent studies have demonstrated that RCC presents an epithelial-mesenchymal transition (EMT) phenotype linked to increased recurrence and decreased survival. EMT is a key characteristic of tumor stem cells (TSCs) along with chemo-resistance and radio-resistance, which are also phenotypic of RCC. Targeting these factors is key to increasing the survival of RCC patients. Doublecortin-like kinase 1 (DCLK1) marks TSCs in pancreatic and colorectal cancer and regulates EMT and stemness. Analysis of the Cancer Genome Atlas' RCC dataset revealed that DCLK1 is overexpressed and dysregulated on the mRNA and epigenetic level in more than 93% of RCC tumors relative to adjacent normal tissue. Immunohistochemistry using α-DCLK1 antibody confirmed overexpression and demonstrated a major increase in immunoreactivity in stage II-III tumors compared to normal kidney and stage I tumors. Small-interfering RNA (siRNA) mediated knockdown of DCLK1 resulted in decreased expression of EMT and pluripotency factors and significantly reduced invasion, migration, focal adhesion, drug-resistance, and clonogenic capacity. These findings suggest that DCLK1 is a novel, overexpressed factor in RCC progression that may be targeted to suppress EMT, metastasis, and stemness in early-stage and advanced RCC to increase patient survival. Moreover, the possibility that DCLK1 may mark a population of tumor stem-like cells in RCC should be further investigated in light of these findings.

BackgroundMore than 80% of intestinal neoplasia is associated with the adenomatous polyposis coli (APC) mutation. Doublecortin-like kinase 1 (Dclk1), a kinase protein, is overexpressed in colorectal cancer and specifically marks tumor stem cells (TSCs) that self-renew and increased the tumor progeny in Apc Min/+ mice. However, the role of Dclk1 expression and its contribution to regulating pro-survival signaling for tumor progression in Apc mutant cancer is poorly understood.MethodsWe analyzed DCLK1 and pro-survival signaling gene expression datasets of 329 specimens from TCGA Colon Adenocarcinoma Cancer Data. The network of DCLK1 and pro-survival signaling was analyzed utilizing the GeneMANIA database. We examined the expression levels of Dclk1 and other stem cell-associated markers, pro-survival signaling pathways, cell self-renewal in the isolated intestinal epithelial cells of Apc Min/+mice with high-grade dysplasia and adenocarcinoma. To determine the functional role of Dclk1 for tumor progression, we knocked down Dclk1 and determined the pro-survival signaling pathways and stemness. We used siRNA technology to gene silence pro-survival signaling in colon cancer cells in vitro. We utilized FACS, IHC, western blot, RT-PCR, and clonogenic (self-renewal) assays.ResultsWe found a correlation between DCLK1 and pro-survival signaling expression. The expression of Dclk1 and stem cell-associated markers Lgr5, Bmi1, and Musashi1 were significantly higher in the intestinal epithelial cells of Apc Min/+mice than in wild-type controls. Intestinal epithelial cells of Apc Min/+mice showed increased expression of pro-survival signaling, pluripotency and self-renewal ability. Furthermore, the enteroids formed from the intestinal Dclk1+ cells of Apc Min/+mice display higher pluripotency and pro-survival signaling. Dclk1 knockdown in Apc Min/+ mice attenuates intestinal adenomas and adenocarcinoma, and decreases pro-survival signaling and self-renewal. Knocking down RELA and NOTCH1 pro-survival signaling and DCLK1 in HT29 and DLD1 colon cancer cells in vitro reduced the tumor cells’ ability to self-renew and survive.ConclusionOur results indicate that Dclk1 is essential in advancing intestinal tumorigenesis. Knocking down Dclk1 decreases tumor stemness and progression and is thus predicted to regulate pro-survival signaling and tumor cell pluripotency. This study provides a strong rationale to target Dclk1 as a treatment strategy for colorectal cancer.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-017-0594-y) contains supplementary material, which is available to authorized users.

Doublecortin-like kinase 1 (Dclk1) is overexpressed in many cancers including colorectal cancer (CRC) and it specifically marks intestinal tumor stem cells. However, the role of Dclk1 in intestinal tumorigenesis in Apc mutant conditions is still poorly understood. We demonstrate that Dclk1 expression and Dclk1+ cells are significantly increased in the intestinal epithelium of elderly ApcMin/+ mice compared to young ApcMin/+ mice and wild type mice. Intestinal epithelial cells of ApcMin/+ mice demonstrate increased pluripotency, self-renewing ability, and EMT. Furthermore, miRNAs are dysregulated, expression of onco-miRNAs are significantly increased with decreased tumor suppressor miRNAs. In support of these findings, knockdown of Dclk1 in elderly ApcMin/+ mice attenuates intestinal adenomas and adenocarcinoma by decreasing pluripotency, EMT and onco-miRNAs indicating that Dclk1 overexpression facilitates intestinal tumorigenesis. Knocking down Dclk1 weakens Dclk1-dependent intestinal processes for tumorigenesis. This study demonstrates that Dclk1 is critically involved in facilitating intestinal tumorigenesis by enhancing pluripotency and EMT factors in Apc mutant intestinal tumors and it also provides a potential therapeutic target for the treatment of colorectal cancer.

BackgroundDoublecortin-like kinase 1 (DCLK1) is emerging as a tumor specific stem cell marker in colorectal and pancreatic cancer. Previous in vitro and in vivo studies have demonstrated the therapeutic effects of inhibiting DCLK1 with small interfering RNA (siRNA) as well as genetically targeting the DCLK1+ cell for deletion. However, the effects of inhibiting DCLK1 kinase activity have not been studied directly. Therefore, we assessed the effects of inhibiting DCLK1 kinase activity using the novel small molecule kinase inhibitor, LRRK2-IN-1, which demonstrates significant affinity for DCLK1.ResultsHere we report that LRRK2-IN-1 demonstrates potent anti-cancer activity including inhibition of cancer cell proliferation, migration, and invasion as well as induction of apoptosis and cell cycle arrest. Additionally we found that it regulates stemness, epithelial-mesenchymal transition, and oncogenic targets on the molecular level. Moreover, we show that LRRK2-IN-1 suppresses DCLK1 kinase activity and downstream DCLK1 effector c-MYC, and demonstrate that DCLK1 kinase activity is a significant factor in resistance to LRRK2-IN-1.ConclusionsGiven DCLK1’s tumor stem cell marker status, a strong understanding of its biological role and interactions in gastrointestinal tumors may lead to discoveries that improve patient outcomes. The results of this study suggest that small molecule inhibitors of DCLK1 kinase should be further investigated as they may hold promise as anti-tumor stem cell drugs.