The RNA binding proteins RBM38 and DND1 are repressed in AML and have a novel function in APL differentiation

Abstract

The RNA binding proteins RBM binding motif protein 38 (RBM38) and DEAD END 1 (DND1) selectively stabilize mRNAs by attenuating RNAse activity or protecting them from micro(mi)RNA-mediated cleavage. Furthermore, both proteins can efficiently stabilize the mRNA of the cell cycle inhibitor p21 CIP1 . Since acute myeloid leukemia (AML) differentiation requires cell cycle arrest and RBM38 as well as DND1 have antiproliferative functions, we hypothesized that decreased RBM38 and DND1 expression may contribute to the differentiation block seen in this disease. We first quantified RBM38 and DND1 mRNA expression in clinical AML patient samples and CD34 + progenitor cells and mature granulocytes from healthy donors. We found significantly lower RBM38 and DND1 mRNA levels in AML blasts and CD34 + progenitor cells as compared to mature neutrophils from healthy donors. Furthermore, the lowest expression of both RBM38 and DND1 mRNA correlated with t(8;21). In addition, neutrophil differentiation of CD34 + cells in vitro with G-CSF (granulocyte colony stimulating factor) resulted in a significant increase of RBM38 and DND1 mRNA levels. Similarly, neutrophil differentiation of NB4 acute promyelocytic leukemia (APL) cells was associated with a significant induction of RBM38 and DND1 expression. To address the function of RBM38 and DND1 in neutrophil differentiation, we generated two independent NB4_RBM38 as well as DND1 knockdown cell lines. Inhibition of both RBM38 and DND1 mRNA significantly attenuated NB4 differentiation and resulted in decreased p21 CIP1 mRNA expression. Our results clearly indicate that expression of the RNA binding proteins RBM38 and DND1 is repressed in primary AML patients, that neutrophil differentiation is dependent on increased expression of both proteins, and that these proteins have a critical role in regulating p21 CIP1 expression during APL differentiation. Highlights RBM38 and DND1 expression is attenuated in primary AML patients  Normal and leukemic neutrophil differentiation induces RBM38 and DND1 expression  New function for the RNA binding proteins RBM38 and DND1 in APL differentiation Keywords: RBM38, DND1, acute myeloid leukemia, acute promyelocytic leukemia, neutrophil differentiation

Generation of a novel mouse strain with conditional, cell‐type specific, expression of DND1

“…DND1 is also expressed in some somatic cells such as in human neutrophils, hematopoietic CD34+ progenitor cells (Wampfler, Federzoni, Torbett, Fey, & Tschan, ) and in normal breast epithelial tissue (Cheng, Pan, Lu, Zhu, & Chen, ). Interestingly, cancer genome sequencing indicates DND1 gene amplification, deletions, or mutations in 1–6% human cancers including those of the kidney, uterus, pancreas, and colon, among others (cBioPortal for Cancer Genomics: http://www.cbioportal.org and TCGA Research Network: http://cancergenome.nih.gov).…”

“…The role of DND1 amplifications, mutations, or ectopic expression in somatic cancer tissues is unclear. In addition, experimental introduction of wild‐type DND1 in human cancer cell lines results in suppression of cancer cell phenotypes, enhanced differentiation and apoptosis (Bhandari et al, ; Cheng et al, ; Liu et al, ; Wampfler et al, ; Xu, Gong, Zhang, Chi, & Wang, ). In contrast, mutated DND1 Ter enhances colon tumorigenesis when combined with the Apc +/Min driver mutation in the mouse (Zechel et al, ).…”

“…The few germ cells that do survive fail to enter cell cycle arrest and give rise to teratomas that are observed in Ter mice on susceptible strain backgrounds (Cook, Coveney, Batchvarov, Nadeau, & Capel, 2009). DND1 is also expressed in some somatic cells such as in human neutrophils, hematopoietic CD34+ progenitor cells (Wampfler, Federzoni, Torbett, Fey, & Tschan, 2016) and in normal breast epithelial tissue (Cheng, Pan, Lu, Zhu, & Chen, 2017 In addition, experimental introduction of wild-type DND1 in human cancer cell lines results in suppression of cancer cell phenotypes, enhanced differentiation and apoptosis (Bhandari et al, 2013;Cheng et al, 2017;Liu et al, 2010;Wampfler et al, 2016;Xu, Gong, Zhang, Chi, & Wang, 2017). In contrast, mutated DND1 Ter enhances colon tumorigenesis when combined with the Apc +/Min driver mutation in the mouse (Zechel et al, 2013).…”

“…DND1-mediated translational regulation helps maintain localized expression of critical proteins in germ cells and in early embryos (Mei et al, 2013;Mishima et al, 2006) and modulates cell proliferation, pluripotency and reprogramming of germ cells to maintain germ cell fate (Cook et al, 2011;Gross-Thebing et al, 2017;Ruthig et al, 2019;Suzuki et al, 2016;Yamaji et al, 2017). The ability of DND1 to function as translational regulator has also been experimentally demonstrated in cancer cells such as in breast cancer cell lines, acute myeloid leukemia cells, and others (Bhandari et al, 2013;Cheng et al, 2017;Liu et al, 2010;Wampfler et al, 2016) where translational upregulation by wildtype DND1 facilitated differentiation and apoptosis.…”

The role of c-Myc-RBM38 loop in the growth suppression in breast cancer

“…As a member of the RNA recognition motif (RRM) family of RBPs, RNA-binding protein 38 (RBM38, also called RNPC1) has been shown to function as a tumor suppressor in breast cancer [5], acute myeloid leukemia [6], colorectal cancer [7], and correlates with improved survival in human ovarian cancer [8]. RBM38 has been implicated in stabilization of p21, p73 and Hu antigen-R (HuR) transcripts and destabilization of mouse double minute 2 homolog (MDM2) transcripts, via binding to AU/U-rich elements (AREs) in the 3′-untranslated region (3′-UTR) of their mRNAs.…”