Recovering false negatives in CRISPR fitness screens with JLOE

OTUD6B regulates KIFC1-dependent centrosome clustering and breast cancer cell survival

Cancer cells often display centrosome amplification, requiring the kinesin KIFC1/HSET for centrosome clustering to prevent multipolar spindles and cell death. In parallel siRNA screens of deubiquitinase enzymes, we identify OTUD6B as a positive regulator of KIFC1 expression that is required for centrosome clustering in triple-negative breast cancer (TNBC) cells. OTUD6B can localise to centrosomes and the mitotic spindle and interacts with KIFC1. In OTUD6B-deficient cells, we see increased KIFC1 polyubiquitination and premature KIFC1 degradation during mitosis. Depletion of OTUD6B increases multipolar spindles without inducing centrosome amplification. Phenotypic rescue is dependent on OTUD6B catalytic activity and evident upon KIFC1 overexpression. OTUD6B is commonly overexpressed in breast cancer, correlating with KIFC1 protein expression and worse patient survival. TNBC cells with centrosome amplification, but not normal breast epithelial cells, depend on OTUD6B to proliferate. Indeed CRISPR-Cas9 editing results in only OTUD6B-/+ TNBC cells which fail to divide and die. As a deubiquitinase that supports KIFC1 expression, allowing pseudo-bipolar cell division and survival of cancer cells with centrosome amplification, OTUD6B has potential as a novel target for cancer-specific therapies.

Genome-wide screening identifies Trim33 as an essential regulator of dendritic cell differentiation

The development of dendritic cells (DCs), including antigen-presenting conventional DCs (cDCs) and cytokine-producing plasmacytoid DCs (pDCs), is controlled by the growth factor Flt3 ligand (Flt3L) and its receptor Flt3. We genetically dissected Flt3L-driven DC differentiation using CRISPR-Cas9-based screening. Genome-wide screening identified multiple regulators of DC differentiation including subunits of TSC and GATOR1 complexes, which restricted progenitor growth but enabled DC differentiation by inhibiting mTOR signaling. An orthogonal screen identified the transcriptional repressor Trim33 (TIF-1γ) as a regulator of DC differentiation. Conditional targeting in vivo revealed an essential role of Trim33 in the development of all DCs, but not of monocytes or granulocytes. In particular, deletion of Trim33 caused rapid loss of DC progenitors, pDCs, and the cross-presenting cDC1 subset. Trim33-deficient Flt3+ progenitors up-regulated pro-inflammatory and macrophage-specific genes but failed to induce the DC differentiation program. Collectively, these data elucidate mechanisms that control Flt3L-driven differentiation of the entire DC lineage and identify Trim33 as its essential regulator.