The association of Greig syndrome and mastocytosis reveals the involvement of the hedgehog pathway in advanced mastocytosis

Mastocytosis is a heterogeneous disease characterized by an abnormal accumulation of mast cells (MCs) in 1 or several organs. Although a somatic KIT D816V mutation is detected in ∼85% of patients, attempts to demonstrate its oncogenic effect alone have repeatedly failed, suggesting that additional pathways are involved in MC transformation. From 3 children presenting with both Greig cephalopolysyndactyly syndrome (GCPS, Mendelian Inheritance in Man [175700]) and congenital mastocytosis, we demonstrated the involvement of the hedgehog (Hh) pathway in mastocytosis. GCPS is an extremely rare syndrome resulting from haploinsufficiency of GLI3, the major repressor of Hh family members. From these familial cases of mastocytosis, we demonstrate that the Hh pathway is barely active in normal primary MCs and is overactive in neoplastic MCs. GLI3 and KIT mutations had a synergistic, tumorigenic effect on the onset of mastocytosis in a GCPS mouse model. Finally, Hh inhibitors suppressed neoplastic MC proliferation in vitro and extend the survival time of mice with aggressive systemic mastocytosis (ASM). This work revealed, for the first time, the involvement of Hh signaling in the pathophysiology of mastocytosis and demonstrated the cooperative effects of the KIT and Hh oncogenic pathways in mice with ASM, leading to the identification of new promising therapeutic targets.

Exon/intron structure and alternative transcripts of the CUTL1 gene

The human CUTL1 gene (Cut-like 1) is a candidate tumor suppressor gene located on chromosome 7 at band 22, a region that is frequently deleted in several human cancers. The gene spans at least 340kb and contains 33 exons. Synthesis of five different transcripts involves two promoter regions, two polyadenylation sites and seven alternative splicing events. The two polyadenylation sites are located at the ends of exons 24 and 33 and are separated by approximately 40kb. Transcription is initiated in two genomic regions, giving rise to alternate first exons which are spliced to a common exon 2. All transcripts contain exons 2 to 14, but differ in their 3' regions. Exon 14 can be spliced alternatively to the beginning or the middle of exon 15, or to exon 25, generating transcripts with exons 15 to 24 or exons 25 to 33. Moreover, exon 16 can be spliced out from the mature transcripts that contain exons 15 to 24. Overall, five distinct transcripts are generated as a result of alternative transcription initiation, splicing and polyadenylation. We discuss potential mechanisms by which alternate polyadenylation site usage may affect alternative splicing events and vice versa.