Functional characterization of p53 molecules expressed in human squamous cell carcinomas of the head and neck

Abstract

Mutation of the p53 tumor suppressor gene has been demonstrated in a large proportion of human head and neck squamous cell carcinomas (HNSCCs) and has been assumed to play a role in the pathogenesis of these tumors, although no formal evidence of functional aberration has been demonstrated. In this study, we isolated cDNA clones encoding the entire p53 coding region from six human HNSCC cell lines that showed aberrant patterns of p53 expression in the parental cells, analyzed their nucleotide sequences, and characterized their function in vivo. cDNAs cloned from four cell lines harbored alterations within the p53 coding sequence (one missense mutation, one missense mutation plus in-frame deletion, one splice donor mutation, and a 1-nt insertion). HN30 cells, which contained wild-type p53 nucleotide sequences, showed a high constitutive level of protein expression. HN26 cells contained wild-type coding sequences but did not express the 53-kDa protein, although the mRNA was transcribed and a molecule of increased molecular mass (70 kDa) was observed by western blotting. Functional studies revealed that none of the four proteins encoded by mutant cDNAs were able to transactivate expression of a reporter plasmid containing a wild-type p53 consensus binding site when cotransfected into p53-null cells, whereas molecules encoded by wild-type p53 cDNAs increased reporter gene expression about a hundredfold over uninduced levels. Co-expression of each mutant cDNA with wild-type p53 cDNA and a wild-type p53-responsive reporter gene demonstrated that each of the proteins encoded by mutant cDNAs harbored some degree of inhibitory activity that varied depending on the mutation present. Thus, aberrant p53 function as a result of mutation or altered expression characterizes oral squamous cell carcinomas. The inhibitory activity of these molecules may be a mechanism for deregulation of the function of co-expressed wild-type p53 that may be of importance during the early stages of tumor development.

Ataxia telangiectasia mutated nuclear localization in head and neck cancer cells is PPP2R2B-dependent

“…1B). P53 statuses of these cell lines were reported elsewhere [25]. We found that the correlation between PPP2R2B mRNA expression and ATMS1981p was not dependent on P53 mutation.…”

Role of GRB2‐associated binder 1 in epidermal growth factor receptor‐induced signaling in head and neck squamous cell carcinoma

“…However, most HNSCC cases are not sensitive to gefitinib, which was nicely reflected in our in vitro model of HN13 cell line, which is derived from a human HNSCC 22. In these cells, the receptor is not constitutively activated, and the antiproliferative response of these cells to gefitinib is rather low, with a high IC 50 that cannot be accomplished in clinic, due to Grade III–IV side effects.…”

Cytotoxic Effect ofCoscinium fenestratumon Human Head and Neck Cancer Cell Line (HN31)

“…5-FU and crude CF extract investigated in this study had cytotoxic effect, and the dose at which 50% cell growth inhibition (IC 50 ) occurs is a measure of the strength or potency of a given compound: the higher the IC 50 , the lower the potency. The IC 50 of 5-FU for the HN31 cell line reported in the present study was 6.6 mg/mL, which is relatively high, presumably due to its mutation of the tumor suppressor gene p53 [ 41 , 47 , 48 ]. In contrast, our preliminary study found that the IC 50 values of 5-FU for the less invasive HNSCC cell lines were substantially lower, for example, 10.26 μ g/mL for HN30 and 24.98 μ g/mL for HN22 (unpublished data), indicating the considerably decreased susceptibility of the HN31 cell line to 5-FU.…”