phosphothreonine and Esophageal-Neoplasms

HPV16 E6 interacts with and degrades tumour suppressor protein TSC2 leading to the phosphorylation of p70 S6 kinase. We studied the association of S6 kinase phosphorylation and HPV16 infection in cervical cancer and esophageal cancer. Immunohistochemistry was used to assess phosphorylated S6 kinase (Thr 389) and phosphorylated S6 (Ser235/236) in 140 cervical cancer and 161 esophageal cancer specimens. Immunohistochemical staining for pS6 kinase and pS6 was significantly more frequent in the HPV16-infected cervical cancer specimens than the HPV16-negative specimens. In contrast, the expression of S6 kinase was similar in both HPV16-positive and -negative samples. The phosphorylation of Akt, the key regulator of S6 kinase, was also detected. Our analysis showed that Akt phosphorylation was unaffected by HPV16 infection. These results together with our previous study suggest that HPV16 modifies S6 kinase activation via mechanism, which activates S6 kinase downstream of Akt function.

Topics: Adult; Aged; Esophageal Neoplasms; Female; Human papillomavirus 16; Humans; Immunohistochemistry; Male; Middle Aged; Papillomavirus Infections; Phosphorylation; Phosphoserine; Phosphothreonine; Proto-Oncogene Proteins c-akt; Ribosomal Protein S6 Kinases, 70-kDa; Uterine Cervical Neoplasms

Although cyclin D1 is overexpressed in a significant number of human cancers, overexpression alone is insufficient to promote tumorigenesis. In vitro studies have revealed that inhibition of cyclin D1 nuclear export unmasks its neoplastic potential. Cyclin D1 nuclear export depends upon phosphorylation of a C-terminal residue, threonine 286, (Thr-286) which in turn promotes association with the nuclear exportin, CRM1. Mutation of Thr-286 to a non-phosphorylatable residue results in a constitutively nuclear cyclin D1 protein with significantly increased oncogenic potential. To determine whether cyclin D1 is subject to mutations that inhibit its nuclear export in human cancer, we have sequenced exon 5 of cyclin D1 in primary esophageal carcinoma samples and in cell lines derived from esophageal cancer. Our work reveals that cyclin D1 is subject to mutations in primary human cancer. The mutations identified specifically disrupt phosphorylation of cyclin D1 at Thr-286, thereby enforcing nuclear accumulation of cyclin D1. Through characterization of these mutants, we also define an acidic residue within the C-terminus of cyclin D1 that is necessary for recognition and phosphorylation of cyclin D1 by glycogen synthase kinase-3 beta. Finally, through construction of compound mutants, we demonstrate that cell transformation by the cancer-derived cyclin D1 alleles correlates with their ability to associate with and activate CDK4. Our data reveal that cyclin D1 is subject to mutations in primary human cancer that specifically disrupt phosphorylation-dependent nuclear export of cyclin D1 and suggest that such mutations contribute to the genesis and progression of neoplastic growth.

Topics: Alleles; Amino Acid Substitution; Animals; Carcinoma; Cell Line; Cell Line, Tumor; Cell Nucleus; Cell Transformation, Neoplastic; Cyclin D; Cyclin D1; Cyclin-Dependent Kinase 4; Cyclins; DNA Mutational Analysis; DNA, Neoplasm; Esophageal Neoplasms; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Mice; Mutation, Missense; Neoplasm Proteins; NIH 3T3 Cells; Phosphorylation; Phosphothreonine; Point Mutation; Protein Processing, Post-Translational; Protein Transport; Recombinant Fusion Proteins; Sequence Deletion; Spodoptera