Novel inactivating mutations of transforming growth factor-? type I receptor gene in head-and-neck cancer metastases

Abstract

Carcinoma cell lines are frequently refractory to transforming growth factor-␤ (TGF␤)-mediated cell cycle arrest. Whether and how TGF␤ signaling is disrupted in the majority of human tumors, however, remains unclear. To investigate whether TGF␤ signaling might be disrupted by inactivation of the key signaling molecule, the TGF␤ type I (T␤R-I) receptor, and whether or not T␤R-I inactivation is associated with late stage disease, we conducted a comprehensive structural analysis of the T␤R-I gene in fine-needle aspirates of 23 head-&-neck cancer metastases. We encountered 4 different mutations of T␤R-I, 3 of which have not been previously identified. In 1 case, we found a somatic intragenic 4-bp deletion predicting for a truncation of the receptor protein. This is the first example of a true loss-of-function mutation of T␤R-I in a human epithelial neoplasm. In 2 other cases, we identified missense mutations located between the juxtamembrane-and serine-threonine kinase domains. One of these resulted in an alanine-to-threonine substitution (A230T), which disrupts receptor signaling activity by causing rapid protein degradation within the endoplasmatic reticulum. This represents a novel mechanism of inactivation of a TGF␤ signaling intermediate. Finally, we identified a serineto-tyrosine substitution at codon 387 (S387Y) in a metastasis but not in the corresponding primary tumor. We had previously shown this S387Y mutant to be predominantly associated with breast cancer metastases and to have a diminished ability to mediate TGF␤-dependent signaling. In aggregate, these findings provide further support for the hypothesis that inactivation of the TGF␤ signaling pathway occurs in a significant subset of human cancers. © 2001 Wiley-Liss, Inc. Key words: transforming growth factor-␤ receptor; mutation; headand-neck cancerThe 25 kDa dimeric polypeptide, transforming growth factor-␤ (TGF␤) is the most potent known inhibitor of normal epithelial cell replication in vitro. 1,2 The TGF␤ signal is transduced by a pair of transmembrane serine-threonine kinase receptors. 3,4 TGF␤ binds primarily to TGF␤ type II receptor (T␤R-II) homodimers, which then form heterotetrameric complexes with 2 TGF␤ type I receptor (T␤R-I) molecules. As a consequence, the T␤R-II kinase phosphorylates the T␤R-I receptor, thereby activating its serinethreonine kinase. In response to T␤R-I activation, 2 cytosolic proteins, Smad2 and Smad3, become transiently associated with and phosphorylated by the T␤R-I kinase. After their activation and release from T␤R-I, Smad 2 and -3 form heteromeric complexes with a third homologue, Smad4. These multimeric Smad complexes are then translocated to the nucleus, bind to DNA in a sequence-specific manner and regulate gene transcription. [3][4][5] The resulting induction of cyclin-dependent kinase (cdk) inhibitors and decreased expression of cyclins, cdks, and the CDK tyrosine phosphatase, Cdc25A, lead to G1 phase cell cycle arrest. 3

An intronic variant of the TGFBR1 gene is associated with carcinomas of the kidney and bladder

“…16 Previously, we identified several novel mutations and genetic variants in the TGFBR1 gene among cancers of the breast, cervix, head/neck and ovary. [17][18][19][20] Taken together, these studies provide strong support for the indispensable role played by the molecular inactivation of TGF-␤ signaling in malignant transformation and implicate TGF-␤ signaling perturbation in human malignancies.To determine whether genetic alterations of TGFBR1 are linked to carcinomas of the human kidney and bladder, we evaluated 151 cases of urinary system carcinoma for somatic or germline mutations of the TGFBR1 gene. We show that somatic mutations of TGFBR1 in patients with cancers of the urinary system were rare, with only one somatic mutation identified in a patient with upper urinary tract TCC.…”

“…16 Previously, we identified several novel mutations and genetic variants in the TGFBR1 gene among cancers of the breast, cervix, head/neck and ovary. [17][18][19][20] Taken together, these studies provide strong support for the indispensable role played by the molecular inactivation of TGF-␤ signaling in malignant transformation and implicate TGF-␤ signaling perturbation in human malignancies.…”

Differences in Smad4 Expression in Human Papillomavirus Type 16–Positive and Human Papillomavirus Type 16–Negative Head and Neck Squamous Cell Carcinoma

“…The exact mechanisms for down-regulation of ThR-II expression are not fully understood; however, ThR-II is frequently mutated in a wide variety of tumor types including HNSCC (5,7). Mutations in ThR-I are less frequent (11,12). Consistent with a tumor suppressor role for the TGF-h signaling pathway, alterations have been identified in other components of the pathway (14 -24).…”

Molecular mechanisms of head and neck cancer

“…These include carcinomas of the breast, prostate, gastrointestinal tract (stomach, colon, and rectum), lung, cervix, liver, and skin. Although mutations of the individual members of the TGF-β pathway have been identified in OSCC and other epithelial tumors, they are relatively rare [70][71][72][73][74]. A more frequent event is a reduction in the expression of TβRII [75].…”