XERODERMA PIGMENTOSUM XPF and Nucleotide Excision Repair Sapna Patel

The Basics Hereditary, autosomal recessive disorder Results in a hypersensitivity to UV rays 1/250,000 have XP in the US

XP leads to a predisposition to cancer Mostly basal and squamous cell carcinomas Certain types can lead to neurological disorders Friedberg, 2001.

What causes XP? 7 different gene abnormalities identified that lead to XP Complementation groups XPA-XPG These genes are crucial for DNA damage repair Friedberg, 2001.

How genes lead to cancer UV radiation leads to DNA damage in the form of pyrimidine dimers and photoproducts.

XP genes respond to damage and carry out NER Each complementation group gene has a specific function in NER Friedberg, 2001.

XPF XPF is part of an endonuclease Forms a heterodimer complex with ERCC1 Together, they make 5’ incision ~24 nt away from damage Friedberg, 2001.

Mutations in XPF gene prevents removal of DNA damage. Sijbers et al, 1996

The damage is transcribed and translated If in a gene for controlling cell proliferation then the result is cancer. Multiple mutations lead up to cancer.

Xeroderma pigmentosum group F Mostly affects Japanese Symptoms are milder than in other types of XP, later onset Few suffer neurological complications

Matsumura et al, 1998.

Identification of XPF ERCC4 had been found to correct NER mutations in hamsters. It was hybridized to human chromosome and found on #16.

Identification of XPF Cosmid clones of chromosome 16 carrying ERCC4 were mapped using fluorescent hybridization. It appeared at 16p13.13-p13.2 as predicted Linkage to the neo gene present in vector indicated that the human gene was cloned. Thompson et al, 1994

S. cerevisiae has a Rad1-Rad10 complex that makes 5’ incision Rad10 was known to be the homolog of ERCC1. A polypeptide copurified with ERCC1 and thought to be the Rad1 homolog Identification of XPF

RT-PCR was used with primers created from Rad1 It was used as a probe to find an ORF on C-terminal similar to that of Rad1. N-terminal of human gene found in database. Assembled Sijbers et al, 1996.

Using in situ hybridization, they found the RAD1 homolog mapped to 16p Identification of XPF Sijbers et al, 1996.

Homolog encodes ERCC4, XPF The homolog was transfected into UV sensitive cells 3 types: UV41 (ERCC4), UVS1 ERCC11), and 43-3B (ERCC1)

The Results Full correction of UV41 Partial correction of UVS1 43-3B cells did not survive Sijbers et al, 1996.

What’s next? There’s no cure for XP Common treatments are excision of carcinomas Prevention using sunscreen (physical and chemical) Some trial w/ repair enzyme