Phillip (Andy) Futreal, Ph.D.

Dissertation research performed under the direction of J. Carl Barrett

ABSTRACT
The development of cancer is a multistep, multigenic process involving both the activation of oncogenes and the inactivation of tumor suppressor genes. This study focused on the physical mapping of tumor suppressor genes on human chromosomes 1q and 17q.  Human chromosome 1q contains a locus capable of inducing senescence (SI) when introduced by microcell fusion into an immortal hamster cell line. Spontaneous nonsenescent revertant hybrids were analyzed for deletions of the introduced human chromosome 1q. Two common regions of deletion were found at 1q25 and 1q42. Flanking markers were determined for each region and were estimated to be 2 centimorgans and 3 centimorgans apart, respectively. The SI phenotype may be a composite of the two mapped loci, or may be represented by either mapped deletion locus. A sequence-tagged site marker map for distal 1q was generated, incorporating 28 markers with an average spacing of 5 centimorgans. The SI locus represents a gene involved in a fundamental step in neoplastic progression, acquisition of uncontrolled proliferation potential.  A tumor suppressor gene for sporadic breast carcinoma was mapped by deletion analysis of to 17q12-q21, a region shown by linkage analysis to contain the BRCA1 gene, which predisposes to familial breast and ovarian carcinoma, suggesting that the sporadic and familial genes are allelic. Frequent allele loss was seen at the thyroid hormone receptor alpha (THRA1) gene. The THRA1 gene was found to be rearranged in the BT474 breast cancer cell line as a result of a large interstitial deletion that fused THRA1 to a novel coding sequence, BTR. Single strand conformation analysis of the THRA1 gene in both sporadic breast carcinomas and familial samples carrying potential germline mutations did not reveal any point mutations, indicating that THRA1 was not the BRCA1 gene. The BRCA1 gene was further mapped to a small region of 17q21. Seven cDNAs expressed in breast were isolated from the region using a novel direct selection procedure. These cDNAs represent seven candidate genes for further mutation analysis as the BRCA1 gene.  This work has provided the framework for the isolation of genes involved in two important facets of neoplastic progression: the control of cellular proliferation potential and the familial predisposition to and development of sporadic breast and ovarian cancers.