Highlights d Cancer-associated fibroblasts contribute to pancreatic cancer heterogeneity d Cancer cells can have a double-positive phenotype: proliferation and invasion d High CAF abundance linked with DP cells enriched for MAPK and STAT3 co-signaling d Intra-tumoral gland types provide tissue heterogeneity linked with clinical outcome

Pancreatic ductal adenocarcinoma (PDAC) lethality is due to metastatic dissemination. Characterization of rare, heterogeneous circulating tumor cells (CTCs) can provide insight into metastasis and guide development of novel therapies. Using the CTC-iChip to purify CTCs from PDAC patients for RNA-seq characterization, we identify three major correlated gene sets, with stemness genes LIN28B/KLF4, WNT5A, and LGALS3 enriched in each correlated gene set; only LIN28B CTC expression was prognostic. CRISPR knockout of LIN28Ban oncofetal RNA-binding protein exerting diverse effects via negative regulation of let-7 miRNAs and other RNA targets-in cell and animal models confers a less aggressive/ metastatic phenotype. This correlates with de-repression of let-7 miRNAs and is mimicked by silencing of downstream let-7 target HMGA2 or chemical inhibition of LIN28B/let-7 binding. Molecular characterization of CTCs provides a unique opportunity to correlated gene set metastatic profiles, identify drivers of dissemination, and develop therapies targeting the "seeds" of metastasis.

Despite recent advances in therapeutic approaches, patients with MLL-rearranged leukemia still have poor outcomes. Here, we find that the RNA-binding protein IGF2BP3, which is overexpressed in MLL-translocated leukemia, strongly amplifies MLL-Af4-mediated leukemogenesis. Deletion of Igf2bp3 significantly increases the survival of mice with MLL-Af4-driven leukemia and greatly attenuates disease, with a minimal impact on baseline hematopoiesis. At the cellular level, MLL-Af4 leukemia-initiating cells require Igf2bp3 for their function in leukemogenesis. At the molecular level, IGF2BP3 regulates a complex posttranscriptional operon governing leukemia cell survival and proliferation. IGF2BP3-targeted mRNA transcripts include important MLL-Af4-induced genes, such as those in the Hoxa locus, and the Ras signaling pathway. Targeting of transcripts by IGF2BP3 regulates both steady-state mRNA levels and, unexpectedly, pre-mRNA splicing. Together, our findings show that IGF2BP3 represents an attractive therapeutic target in this disease, providing important insights into mechanisms of posttranscriptional regulation in leukemia.

BMP4/7-dependent expression of inhibitor of differentiation/DNA binding (Id) proteins 1 and 3 has been implicated in tumor progression and poor prognosis of malignant melanoma patients. Hyaluronic acid (HA), a pericellular matrix component, supports BMP7 signalling in murine chondrocytes through its receptor CD44. However, its role in regulating BMP signalling in melanoma is not clear. In this study we found that depletion of endogenously-produced HA by hyaluronidase treatment or by inhibition of HA synthesis by 4-methylumbelliferone (4-MU) resulted in reduced BMP4/7-dependent Id1/3 protein expression in mouse melanoma B16-F10 and Ret cells. Conversely, exogenous HA treatment increased BMP4/7-dependent Id1/3 protein expression. Knockdown of CD44 reduced BMP4/7-dependent Id1/3 protein expression, and attenuated the ability of exogenous HA to stimulate Id1 and Id3 expression in response to BMP. Co-IP experiments demonstrated that CD44 can physically associate with the BMP type II receptor (BMPR) ACVR2B. Importantly, we found that coordinate expression of Id1 or Id3 with HA synthases HAS2, HAS3, and CD44 is associated with reduced overall survival of cutaneous melanoma patients. Our results suggest that HA-CD44 interactions with BMPR promote BMP4/7-dependent Id1/3 protein expression in melanoma, contributing to reduced survival in melanoma patients.