PUMILIO Proteins in Colorectal Cancer: Tumor Growth Promoting Function and Potential as Therapeutic Targets

PUMILIO (PUM) proteins belong to the highly conserved PUF family post-transcriptional regulators involved in diverse biological processes. However, their function in carcinogenesis remains under explored. Here, we found that the expression of Pum1 and Pum2 are increased in clinical colorectal cancer (CRC). Intestine-specific knockout of Pum1 and Pum2 significantly inhibited the progression of colitis associated cancer in the AOM/DSS model. Knockout or knockdown of Pum1 and/or Pum2 resulted in a significant decrease in the tumorigenicity. In addition, delayed G1/S transition was observed. We identified p21/Cdkn1a as direct target of PUM1, and abrogation of the PUM1 binding site in p21 resulted in decreased tumor cell growth as well as delayed G1/S transition. Furthermore, intravenous injection of nanoparticle-encapsulated anti-Pum1 and Pum2 siRNAs reduced colorectal tumor growth in murine orthotopic colon cancer models. These findings reveal a tumor growth promoting role of PUM proteins in CRC and its potential as therapeutic targets.

Antagonistic control of Caenorhabditis elegans germline stem cell proliferation and differentiation by PUF proteins FBF-1 and FBF-2

Stem cells support tissue maintenance, but the mechanisms that coordinate the rate of stem cell self-renewal with differentiation at a population level remain uncharacterized. We find that two PUF family RNA-binding proteins FBF-1 and FBF-2 have opposite effects on Caenorhabditis elegans germline stem cell dynamics: FBF-1 restricts the rate of meiotic entry, while FBF-2 promotes both cell division and meiotic entry rates. Antagonistic effects of FBFs are mediated by their distinct activities toward the shared set of target mRNAs, where FBF-1-mediated post-transcriptional control requires the activity of CCR4-NOT deadenylase, while FBF-2 is deadenylase-independent and might protect the targets from deadenylation. These regulatory differences depend on protein sequences outside of the conserved PUF family RNA-binding domain. We propose that the opposing FBF-1 and FBF-2 activities serve to modulate stem cell division rate simultaneously with the rate of meiotic entry.

PUF family proteins FBF-1 and FBF-2 regulate germline stem and progenitor cell proliferation and differentiation in C. elegans

ABSTRACTStem cells support tissue maintenance, but the mechanisms that balance the rate of stem cell self-renewal with differentiation at a population level remain uncharacterized. Through investigating the regulation of germline stem cells by two PUF family RNA-binding proteins FBF-1 and FBF-2 in C. elegans, we find that FBF-1 restricts differentiation, while FBF-2 promotes both proliferation and differentiation. FBFs act on a shared set of target mRNAs; however, FBF-1 destabilizes target transcripts, while FBF-2 promotes their accumulation. These regulatory differences result in complementary effects of FBFs on stem cells. We identify a mitotic cyclin as one of the targets affecting stem cell homeostasis. FBF-1-mediated translational control requires the activity of CCR4-NOT deadenylase. Distinct abilities of FBFs to cooperate with CCR4-NOT depend on protein sequences outside of the conserved PUF family RNA-binding domain. We propose that the combination of FBF activities regulates the dynamics of germline stem cell proliferation and differentiation.

The target specificity of the RNA binding protein Pumilio is determined by distinct co-factors

Puf family proteins are translational regulators essential to a wide range of biological processes, including cell fate specification, stem cell self-renewal, and neural function. Yet, despite being associated with hundreds of RNAs, the underlying mechanisms of Puf target specification remain to be fully elucidated. In Drosophila, Pumilio – a sole Puf family protein – is known to collaborate with cofactors Nanos (Nos) and Brain Tumor (Brat); however, their roles in target specification are not clearly defined. Here, we identify Bag-of-marbles (Bam) as a new Pum cofactor in repression of Mothers against dpp (mad) mRNAs, for which Nos is known to be dispensable. Notably, our data show that Nos (but not Bam) was required for Pum association with hunchback (hb) mRNAs, a well-known target of Pum and Nos. In contrast, Bam (but not Nos) was required for Pum association with mad mRNAs. These findings show for the first time that Pum target specificity is determined not independently but in collaboration with cofactors.