Dsh homolog DVL3 mediates resistance to IGFIR inhibition by regulating IGF-RAS signaling

Drugs that inhibit insulin-like growth factor 1 (IGFI) receptor IGFIR were encouraging in early trials, but predictive biomarkers were lacking and the drugs provided insufficient benefit in unselected patients. In this study, we used genetic screening and downstream validation to identify the WNT pathway element DVL3 as a mediator of resistance to IGFIR inhibition. Sensitivity to IGFIR inhibition was enhanced specifically in vitro and in vivo by genetic or pharmacologic blockade of DVL3. In breast and prostate cancer cells, sensitization tracked with enhanced MEK-ERK activation and relied upon MEK activity and DVL3 expression. Mechanistic investigations showed that DVL3 is present in an adaptor complex that links IGFIR to RAS, which includes Shc, growth factor receptor-bound-2 (Grb2), son-of-sevenless (SOS), and the tumor suppressor DAB2. Dual DVL and DAB2 blockade synergized in activating ERKs and sensitizing cells to IGFIR inhibition, suggesting a nonredundant role for DVL3 in the Shc-Grb2-SOS complex. Clinically, tumors that responded to IGFIR inhibition contained relatively lower levels of DVL3 protein than resistant tumors, and DVL3 levels in tumors correlated inversely with progression-free survival in patients treated with IGFIR antibodies. Because IGFIR does not contain activating mutations analogous to EGFR variants associated with response to EGFR inhibitors, we suggest that IGF signaling achieves an equivalent integration at the postreceptor level through adaptor protein complexes, influencing cellular dependence on the IGF axis and identifying a patient population with potential to benefit from IGFIR inhibition.

Intratumoral hypoxia as the genesis of genetic instability and clinical prognosis in prostate cancer

Intratumoral hypoxia is prevalent in many solid tumors and is a marker of poor clinical prognosis in prostate cancer. The presence of hypoxia is associated with increased chromosomal instability, gene amplification, downregulation of DNA damage repair pathways, and altered sensitivity to agents that damage DNA. These genomic changes could also lead to oncogene activation or tumor suppressor gene inactivation during prostate cancer progression. We review here the concept of repair-deficient hypoxic tumor cells that can adapt to low oxygen levels and acquire an aggressive "unstable mutator" phenotype. We speculate that hypoxia-induced genomic instability may also be a consequence of aberrant mitotic function in hypoxic cells, which leads to increased chromosomal instability and aneuploidy. Because both hypoxia and aneuploidy are prognostic factors in prostate cancer, a greater understanding of these biological states in prostate cancer may lead to novel prognostic and predictive tests and drive new therapeutic strategies in the context of personalized cancer medicine.

Activating BRAF and PIK3CA mutations cooperate to promote anaplastic thyroid carcinogenesis

UNLABELLED Thyroid malignancies are the most common type of endocrine tumors. Of the various histologic subtypes, anaplastic thyroid carcinoma (ATC) represents a subset of all cases but is responsible for a significant proportion of thyroid cancer-related mortality. Indeed, ATC is regarded as one of the more aggressive and hard to treat forms of cancer. To date, there is a paucity of relevant model systems to critically evaluate how the signature genetic abnormalities detected in human ATC contribute to disease pathogenesis. Mutational activation of the BRAF protooncogene is detected in approximately 40% of papillary thyroid carcinoma (PTC) and in 25% of ATC. Moreover, in ATC, mutated BRAF is frequently found in combination with gain-of-function mutations in the p110 catalytic subunit of PI3'-Kinase (PIK3CA) or loss-of-function alterations in either the p53 (TP53) or PTEN tumor suppressors. Using mice with conditional, thyrocyte-specific expression of BRAF(V600E), we previously developed a model of PTC. However, as in humans, BRAF(V600E)-induced mouse PTC is indolent and does not lead to rapid development of end-stage disease. Here, we use mice carrying a conditional allele of PIK3CA to demonstrate that, although mutationally activated PIK3CA(H1047R) is unable to drive transformation on its own, when combined with BRAF(V600E) in thyrocytes, this leads to development of lethal ATC in mice. Combined, these data demonstrate that the BRAF(V600E) cooperates with either PIK3CA(H1074R) or with silencing of the tumor-suppressor PTEN, to promote development of anaplastic thyroid carcinoma. IMPLICATIONS This genetically relevant mouse model of ATC will be an invaluable platform for preclinical testing of pathway-targeted therapies for the prevention and treatment of thyroid carcinoma.

Inactivation of the p53-KLF4-CEBPA Axis in Acute Myeloid Leukemia.

PURPOSE In acute myeloid leukemia (AML), the transcription factors CEBPA and KLF4 as well as the universal tumor suppressor p53 are frequently deregulated. Here, we investigated the extent of dysregulation, the molecular interactions, and the mechanisms involved. EXPERIMENTAL DESIGN One hundred ten AML patient samples were analyzed for protein levels of CEBPA, KLF4, p53, and p53 modulators. Regulation of CEBPA gene expression by KLF4 and p53 or by chemical p53 activators was characterized in AML cell lines. RESULTS We found that CEBPA gene transcription can be directly activated by p53 and KLF4, suggesting a p53-KLF4-CEBPA axis. In AML patient cells, we observed a prominent loss of p53 function and concomitant reduction of KLF4 and CEBPA protein levels. Assessment of cellular p53 modulator proteins indicated that p53 inactivation in leukemic cells correlated with elevated levels of the nuclear export protein XPO1/CRM1 and increase of the p53 inhibitors MDM2 and CUL9/PARC in the cytoplasm. Finally, restoring p53 function following treatment with cytotoxic chemotherapy compounds and p53 restoring non-genotoxic agents induced CEBPA gene expression, myeloid differentiation, and cell-cycle arrest in AML cells. CONCLUSIONS The p53-KLF4-CEBPA axis is deregulated in AML but can be functionally restored by conventional chemotherapy and novel p53 activating treatments. Clin Cancer Res; 22(3); 746-56. ©2015 AACR.

The kinases NDR1/2 act downstream of the Hippo homolog MST1 to mediate both egress of thymocytes from the thymus and lymphocyte motility

The serine and threonine kinase MST1 is the mammalian homolog of Hippo. MST1 is a critical mediator of the migration, adhesion, and survival of T cells; however, these functions of MST1 are independent of signaling by its typical effectors, the kinase LATS and the transcriptional coactivator YAP. The kinase NDR1, a member of the same family of kinases as LATS, functions as a tumor suppressor by preventing T cell lymphomagenesis, which suggests that it may play a role in T cell homeostasis. We generated and characterized mice with a T cell-specific double knockout of Ndr1 and Ndr2 (Ndr DKO). Compared with control mice, Ndr DKO mice exhibited a substantial reduction in the number of naïve T cells in their secondary lymphoid organs. Mature single-positive thymocytes accumulated in the thymus in Ndr DKO mice. We also found that NDRs acted downstream of MST1 to mediate the egress of mature thymocytes from the thymus, as well as the interstitial migration of naïve T cells within popliteal lymph nodes. Together, our findings indicate that the kinases NDR1 and NDR2 function as downstream effectors of MST1 to mediate thymocyte egress and T cell migration.

Loss of Raf-1 kinase inhibitor protein (RKIP) is strongly associated with high-grade tumor budding and correlates with an aggressive phenotype in pancreatic ductal adenocarcinoma (PDAC)

BACKGROUND Raf-1 kinase inhibitor protein (RKIP) has emerged as a significant metastatic suppressor in a variety of human cancers and is known to inhibit Ras/Raf/MEK/ERK signaling. By suppressing the activation of the NFkB/SNAIL circuit, RKIP can regulate the induction of epithelial-mesenchymal transition (EMT). The aim of this study was to evaluate RKIP expression and to determine its association with clinicopathological features, including EMT in form of tumor budding in pancreatic ductal adenocarcinoma (PDAC). METHODS Staining for RKIP was performed on a multipunch Tissue Microarray (TMA) of 114 well-characterized PDACs with clinico-pathological, follow-up and adjuvant therapy information. RKIP-expression was assessed separately in the main tumor body and in the tumor buds. Another 3 TMAs containing normal pancreatic tissue, precursor lesions (Pancreatic Intraepithelial Neoplasia, PanINs) and matched lymph node metastases were stained in parallel. Cut-off values were calculated by receiver operating characteristic (ROC) curve analysis. RESULTS We found a significant progressive loss of RKIP expression between normal pancreatic ductal epithelia (average: 74%), precursor lesions (PanINs; average: 37%), PDAC (average 20%) and lymph node metastases (average 8%, p<0.0001). RKIP expression was significantly lower in tumor buds (average: 6%) compared to the main tumor body (average 20%; p<0.005). RKIP loss in the tumor body was marginally associated with advanced T-stage (p=0.0599) as well as high-grade peritumoral (p=0.0048) and intratumoral budding (p=0.0373). RKIP loss in the buds showed a clear association with advanced T stage (p=0.0089). CONCLUSIONS The progressive loss of RKIP seems to play a major role in the neoplastic transformation of pancreas, correlates with aggressive features in PDAC and is associated with the presence of EMT in form of tumor budding.