Kirk, N. A. | bioRxiv Science

bioRxiv2023

Robo1 loss has pleiotropic effects on postnatal development and survival

Roundabout guidance receptor 1 (Robo1) is known to function during midbrain development in mice, but its postnatal role remains poorly defined in part due to the perinatal lethality of the mice lacking the gene. Here, we describe the postnatal phenotypes of Robo1-/- mice in the B6/129s genetic background. Robo1-/- mice had both a slower growth rate and shorter lifespan compared to Robo1+/+ littermates. Skin histological analysis revealed that Robo1-/- mice displayed increased wrinkles, enlarged sebaceous glands, and a reduced subcutaneous fat layer. Robo1-/- mice displayed accelerated hair graying in line with an observed overall decrease in melanin production. Although both growth hormone (GH) and insulin-like growth hormone 1 (IGF-1) were suppressed in Robo1-deficient mice at 3 weeks of age, they were expressed at similar levels to Robo1 intact mice at 7 weeks of age. These findings suggest that Robo1-mediated hormone regulation is required for normal growth during the early stages of puberty and may provide a crucial timepoint at which to examine the molecular mechanisms of pituitary disorders.

developmental biology↗

bioRxiv2023

CRACD, a gatekeeper restricting proliferation, heterogeneity, and immune evasion of small cell lung cancer

Small cell lung cancer (SCLC) is aggressive with limited therapeutic options. Despite recent advances in targeted therapies and immunotherapies, therapy resistance is a recurring issue, which might be partly due to tumor cell plasticity, a change in cell fate. Nonetheless, the mechanisms underlying tumor cell plasticity and immune evasion in SCLC remain elusive. CRACD, a capping protein inhibitor that promotes actin polymerization, is frequently inactivated in SCLC. Cracd knockout (KO) transforms preneoplastic cells into SCLC tumor-like cells and promotes in vivo SCLC development driven by Rb1, Trp53, and Rbl2 triple KO. Cracd KO induces neuroendocrine (NE) plasticity and increases tumor cell heterogeneity of SCLC tumor cells via dysregulated NOTCH1 signaling by actin cytoskeleton disruption. CRACD depletion also reduces nuclear actin and induces EZH2-mediated H3K27 methylation. This nuclear event suppresses the MHC-I genes and thereby depletes intratumoral CD8+ T cells for accelerated SCLC tumorigenesis. Pharmacological blockade of EZH2 inhibits CRACD-negative SCLC tumorigenesis by restoring MHC-I expression and immune surveillance. Unsupervised single-cell transcriptomics identifies SCLC patient tumors with concomitant inactivation of CRACD and downregulated MHC-I pathway. This study defines CRACD, an actin regulator, as a tumor suppressor that limits cell plasticity and immune evasion and proposes EZH2 blockade as a viable therapeutic option for CRACD-negative SCLC.

cancer biology↗