Hammer, R. E. | Search bioRxiv

bioRxiv2023

Target-directed microRNA degradation regulates developmental microRNA expression and embryonic growth in mammals

MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression that play critical roles in development and disease. Target-directed miRNA degradation (TDMD), a pathway in which miRNAs that bind to specialized targets with extensive complementarity are rapidly decayed, has emerged as a potent mechanism of controlling miRNA levels. Nevertheless, the biological role and scope of miRNA regulation by TDMD in mammals remains poorly understood. To address these questions, we generated mice with constitutive or conditional deletion of Zswim8, which encodes an essential TDMD factor. Loss of Zswim8 resulted in developmental defects in heart and lung, growth restriction, and perinatal lethality. Small RNA sequencing of embryonic tissues revealed widespread miRNA regulation by TDMD and greatly expanded the known catalog of miRNAs regulated by this pathway. These experiments also uncovered novel features of TDMD-regulated miRNAs, including their enrichment in co-transcribed clusters and examples in which TDMD underlies arm switching, a phenomenon wherein the dominant strand of a miRNA precursor changes in different tissues or conditions. Importantly, deletion of two miRNAs, miR-322 and miR-503, rescued growth of Zswim8 null embryos, directly implicating the TDMD pathway as a regulator of mammalian body size. These data illuminate the broad landscape and developmental role of TDMD in mammals.

molecular biology↗

bioRxiv2021

Endosomal Acidification by NHE6-depletion Corrects ApoE4-mediated Synaptic Impairments and Reduces Amyloid Plaque Load

Apolipoprotein E4 (ApoE4) is the most important and prevalent risk factor for late-onset Alzheimers disease (AD). The isoelectric point of ApoE4 matches the pH of the early endosome (EE), causing its delayed dissociation from ApoE receptors and hence impaired endolysosomal trafficking, disruption of synaptic homeostasis and reduced amyloid clearance. We have shown that enhancing endosomal acidification by inhibiting the EE-specific sodium-hydrogen exchanger NHE6 restores vesicular trafficking and normalizes synaptic homeostasis. Remarkably and unexpectedly, loss of NHE6 effectively suppressed amyloid deposition even in the absence of ApoE4, suggesting that accelerated acidification of early endosomes caused by the absence of NHE6 occludes the effect of ApoE on amyloid plaque formation. NHE6 suppression or inhibition may thus be a universal, ApoE-independent approach to prevent amyloid buildup in the brain. These findings suggest a novel therapeutic approach for the prevention of AD by which partial NHE6 inhibition reverses the ApoE4 induced endolysosomal trafficking defect and reduces amyloid.

neuroscience↗

bioRxiv2018

Modulation of mutant KrasG12D-driven lung tumorigenesis in vivo by gain or loss of PCDH7 function

PROTOCADHERIN 7 (PCDH7), a transmembrane receptor and member of the Cadherin superfamily, is frequently overexpressed in lung adenocarcinoma and is associated with poor clinical outcome. While PCDH7 was recently shown to promote transformation and facilitate brain metastasis in lung and breast cancers, decreased PCDH7 expression has also been documented in colorectal, gastric, and invasive bladder cancers. These data suggest context-dependent functions for PCDH7 in distinct tumor types. Given that PCDH7 is a potentially targetable molecule on the surface of cancer cells, further investigation of its role in tumorigenesis in vivo is needed to evaluate the therapeutic potential of its inhibition. Here we report the analysis of novel PCDH7 gain- and loss-of-function mouse models and provide compelling evidence that this cell-surface protein acts as a potent lung cancer driver. Employing a Cre-inducible transgenic allele, we demonstrated that enforced PCDH7 expression significantly accelerates KrasG12D-driven lung tumorigenesis and potentiates MAPK pathway activation. Furthermore, we performed in vivo somatic genome editing with CRISPR/Cas9 in KrasLSL-G12D; Tp53fl/fl (KP) mice to assess the consequences of PCDH7 loss of function. Inactivation of PCDH7 in KP mice significantly reduced lung tumor development, prolonged survival, and diminished phospho-activation of ERK1/2. Together, these findings establish a critical oncogenic function for PCDH7 in vivo and highlight the therapeutic potential of PCDH7 inhibition for lung cancer. Moreover, given recent reports of elevated or reduced PCDH7 in distinct tumor types, the new inducible transgenic model described here provides a robust experimental system for broadly elucidating the effects of PCDH7 overexpression in vivo.\n\nAUTHOR SUMMARYLung cancer is the leading cause of cancer-associated deaths worldwide. PROTOCADHERIN 7 (PCDH7), cell surface protein and member of the Cadherin superfamily, is frequently overexpressed in lung adenocarcinomas and is associated with poor clinical outcome. Nevertheless, it has yet to be shown in vivo whether PCDH7 plays a role in the initiation and progression of lung cancer, and whether it represents an actionable therapeutic target. Here we demonstrate, using a novel transgenic mouse model, that PCDH7 overexpression accelerates KrasG12D-driven lung tumorigenesis. Furthermore, we validate PCDH7 as a therapeutic target by knocking it out using in vivo somatic genome editing in the KrasLSL-G12D; Tp53fl/fl (KP) model. Our results provide new insight into the mechanisms that drive lung cancer pathogenesis and, because targeting oncogenic cell-surface proteins with antibodies has proven to be a highly effective anti-cancer therapeutic strategy, establish a new target for cancer treatment. Moreover, given recent reports of elevated or reduced PCDH7 in distinct tumor types, the transgenic PCDH7 model described here provides a robust experimental system for elucidating the effects of PCDH7 overexpression in different in vivo settings. This model will also provide an ideal system for future testing of therapeutics directed at PCDH7.

cancer biology↗