Susceptibility of epithelial cells cultured from different regions of human cervix to HPV16-induced immortalization

<div><p>Persistent infection with high-risk human papillomavirus (HPV) is a major risk factor for cervical cancer. Greater than 90% of these cancers originate in the cervical transformation zone (TZ), a narrow region of metaplastic squamous epithelium that develops at the squamocolumnar junction between the ectocervix and endocervix. It is unclear why the TZ has high susceptibility to malignant transformation and few studies have specifically examined cells from this region. We hypothesized that cells cultured from TZ are more susceptible to cellular immortalization, an alteration that contributes to malignant development. We cultured primary epithelial cells from each region of human cervix (ectocervix, endocervix and TZ) and measured susceptibility to immortalization after transfection with the complete HPV-16 genome or infection of HPV16 E6/E7 retroviruses. Cells cultured from each cervical region expressed keratin markers (keratin 14 and 18) that confirmed their region of origin. In contrast to our prediction, cells from TZ were equally susceptible to immortalization as cells from ectocervix or endocervix. Thus, increased susceptibility of the TZ to cervical carcinogenesis is not due to increased frequency of immortalization by HPV-16. We developed a series of HPV16-immortalized cell lines from ectocervix, endocervix and TZ that will enable comparisons of how these cells respond to factors that promote cervical carcinogenesis.</p></div

Keratin expression in HPV-immortalized cell lines.

<p>A. Immunofluorescence staining for K14 and K18 in TZ, ectocervix and endocervix-derived immortalized CX16-RV2 cell lines. B. Quantitative analysis of K14 and K18 staining intensity in 12 HPV16 immortalized cervical cell lines. Bars represent the mean ± standard error of four experiments using samples from different donors. The asterisks show statistical differences [*** P < 0.001].</p

Structure and histology of the cervical TZ.

<p>A. Schematic representation of the cervix showing the TZ between ectocervix and endocervix. B. Histology of the cervical TZ showing the stratified squamous epithelium and underlying Nabothian cysts. C. Schematic showing the surface features of ectocervix, endocervix and TZ that aid in tissue dissection. The ectocervix is easily identified because the surface is smooth, white, and shiny with no mucous. The endocervix surface is rough, red in color, and covered with mucous. The TZ contains Nabothian cysts (swollen glands due to occlusion of ducts by squamous metaplasia). These large cysts are easily visible and diagnostic for the TZ. D. Photograph of a typical cervical specimen showing each region.</p

Cell morphology and keratin expression of monolayer cervical cell cultures.

<p>A. Phase contrast microscopy of primary human cervical cells from each region showing different cell morphology. B. K14 and K18 immunostaining showing different expression in cell culture <i>in vitro</i>. C. K17 and MMP7 immunostaining of cells cultured from each region of cervix. Irrelevant primary antibodies were used as the negative control for immunostaining.</p

Properties of HPV16-immortalized cell lines.

<p>Properties of HPV16-immortalized cell lines.</p

Infection and immortalization by retroviruses encoding HPV16 <i>E6</i>/<i>E7</i>.

<p>A. Infection efficiency of cells from ectocervix, TZ and endocervix. The bars represent the mean ± standard error of eight experiments using samples from different donors. B. Immortalization efficiency of cervical cells from each region that was normalized for differences in infection rate. Bars represent the mean ± standard error of eight experiments using samples from different donors. The asterisks show statistical differences [** P < 0.01; *** P < 0.001].</p