The Early HPV16 Proteins Can Regulate mRNA Levels of Cell Cycle Genes in Human Cervical Carcinoma Cells by p53-Independent Mechanisms

Abstract

Cervical carcinoma-associated human papillomavirus type 16 (HPV16) encodes E6 and E7 oncoproteins which inactivate p53 and Rb, respectively, but these interactions are not sufficient to account for the oncogenic potential of the virus. Several viral promoters were shown to be regulated by E6 and E7. To identify genes as cellular targets of the HPV16 early proteins, we transfected a new HPV-negative and p53-mutated cervical carcinoma-derived cell line with either the HPV16 full-length genome or the HPV16 E6 gene. HPV16 clones but not 16E6 clones showed a decreased doubling time that was not related to the viral DNA and mRNA patterns. In exponentially growing cells as well as in cells synchronized by serum starvation, expression of the E6 gene was associated with upregulation of the c-fos and c-jun proto-oncogenes and with downregulation of the c-Ha-ras gene. Furthermore, a viral gene other than E6 may be involved in downregulation of p53 because a reduced mRNA level at the G1/S transition was observed only in HPV16-cells. The present study on natural host cells indicates p53-independent transcriptional modulations of cell cycle regulatory genes related to HPV16 E6 and E7 expression.

The Human Papillomavirus 16 E6 Protein Binds to Fas-associated Death Domain and Protects Cells from Fas-triggered Apoptosis

“…Following elution from the beads, separation by SDS-PAGE, and transfer to a membrane, the membrane was blotted with anti-FADD. Lanes [5][6][7] show that approximately equivalent amounts of the indicated FADD variants were used for each incubation. 2nd panel, the same filter as described above was reblotted with antibodies directed against GST.…”

“…E7 is best known for its ability to bind to and inactivate the retinoblastoma protein, whereas E6 was initially recognized for its ability to bind to and mediate the rapid, ubiquitin-dependent degradation of the tumor suppressor p53 (2). Although this ability clearly contributes to its oncogenic potential, E6 has additional biological and transforming activities that appear to be independent of p53 (3)(4)(5)(6)(7)(8)(9)(10)(11). Mechanistically, these activities are a consequence of the interactions of E6 with cellular proteins, and results from many laboratories, including our own, provide evidence that E6 does, in fact, interact with a wide variety of cellular proteins involved in a number of cellular functions (reviewed in Ref.…”

Destruxin E, a Cyclodepsipeptide Antibiotic, Reduces Cyclin D1 Levels and Inhibits Anchorage-Independent Growth of v-Ki-ras-Expressed pMAM-ras-REF Cells

“…Some tumor cell lines are synchronized by serum starvation. [9][10][11] rasREF cells stopped proliferating 24 h after serum starvation and were synchronized at the G0/G1 phase in 31 h. The synchronized cells were allowed to progress to the S phase upon the addition of serum. DNA synthesis was measured as a marker of S phase, using bromodeoxyuridine 16 h after serum addition.…”

The Human Papillomavirus 16 E6 Protein Binds to Tumor Necrosis Factor (TNF) R1 and Protects Cells from TNF-induced Apoptosis

“…The E7 protein functions by binding to and inactivating the tumor suppressor protein Rb, while E6 is best known for mediating the rapid degradation of the tumor suppressor p53. Whereas this activity clearly contributes to the oncogenic potential of E6, this viral protein has additional biological and transforming activities that appear to be independent of p53 (2)(3)(4)(5)(6)(7)(8)(9)(10). Mechanisms of E6 action probably involve interaction with cellular proteins, and indeed, the HPV E6 protein has been reported to interact with a number of cellular proteins in addition to p53 and E6-AP (reviewed in Ref.…”