Several PATCHED1 missense mutations display activity in patched1-deficient fibroblasts

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• Mutations in patched1 (ptc1) are linked to human birth defects and cancer.
• Ptc1 acts as a receptor for Hedgehog (Hh) signaling proteins, regulating target gene transcription, including its own.
• Ptc1's repression of Hh target genes involves modulation of Gli transcription factors.

Purpose of the Study:

• To investigate Hedgehog (Hh) signal transduction using mammalian cell lines with reduced Ptc1 function.
• To analyze the impact of ptc1 mutations on Hh pathway activity and gene expression.
• To understand the functional consequences of PTCH1 mutations in disease contexts.

Main Methods:

• Established mammalian cell lines (embryonic fibroblasts) from mice heterozygous or homozygous for a ptc1 mutation introducing lacZ reporter.
• Utilized Sonic Hedgehog (Shh) and Gli-1 to stimulate Hh signaling and assess ptc1-lacZ expression.
• Introduced wild-type ptc1 transgenes and expressed Ptc1 protein fragments and missense mutants to evaluate complementation and activity.

Main Results:

• Homozygous ptc1 cells showed high ptc1-lacZ expression without Hh stimulation, while heterozygotes required induction.
• ptc1-lacZ expression was cell density-dependent in homozygotes and Hh-stimulated heterozygotes, but density-independent with Gli1 activation.
• Wild-type ptc1 transgene reduced ptc1-lacZ expression in homozygous cells; Ptc1 halves matured and were active when co-expressed, and missense mutants retained significant function.

Conclusions:

• Reduced PTCH1 activity, even by small amounts, may contribute to certain tumors and disease phenotypes.
• The functional integrity of both Ptc1 halves is necessary for proper protein maturation and activity.
• PTCH1 missense mutations can retain significant function, suggesting complex genotype-phenotype relationships in diseases associated with PTCH1.