Isoform-specific aPKC renders primary cilia dispensable for Hedgehog signaling and basal cell carcinoma growth

Primary cilia loss is a common feature of advanced cancers. While primary cilia are necessary to initiate Hedgehog (HH)-driven cancers, how HH pathway activity is maintained in advanced cancers devoid of primary cilia is unclear. Here, we find that HH-driven basal cell carcinoma (BCC) accumulates mutations in Alström and Usher syndrome genes. Loss of Alström and Usher syndrome gene expression, which are common underlying causes of deafness and blindness, suppresses primary ciliogenesis and HH signaling but enhances expression of atypical protein kinase C iota/lambda (aPKC), a GLI1 kinase necessary for advanced BCC growth. We show that aPKC expression is inversely correlated with primary ciliogenesis and that superficial BCCs display less primary cilia and higher aPKC expression, with the opposite trend in nodular BCC subtypes. Surprisingly, a constitutively active isoform of aPKC but not full-length protein drives HH pathway activity. Overexpression of the constitutively active aPKC variant can maintain HH pathway activity and tumor growth in the absence of primary cilia. Our results suggest tumors enhance isoform-specific expression of aPKC to prevent mutation-induced cessation of tumor growth.