Quantitation and localization of cellular retinol-binding protein in squamous-cell carcinomas of the cervix uteri and of the oral cavity

The Ki67+ proliferation index correlates with increased cellular retinol-binding protein-1 and the coordinated loss of plakophilin-1 and desmoplakin during progression of cervical squamous lesions

AIMS

To investigate the modulation of cellular retinol-binding protein (CRBP)-1 and the desmosomal plaque proteins plakophilin (PKP)-1 and desmoplakin (DP) in correlation with the Ki67+ proliferation index (PI) during the progression of cervical squamous intraepithelial lesions (SIL) to squamous cell carcinoma (SCC).

METHODS

Using in situ imaging by brightfield and confocal laser scanning microscopy, the expression of CRBP-1 protein and transcripts, PKP-1, DP and the Ki67 PI were analysed in 38 low-grade (L) SIL, 56 high-grade (H) SIL, 49 SCC, 30 control cervices and 10 human papillomavirus-positive condylomatous lesions.

RESULTS

CRBP-1+ cells increased from 11.4% in the normal cervix to 80.3% in LSILs, 92.3% in HSILs and slightly decreased to 78.3% in invasive SCCs (P = 0.0001) in close association with the Ki67 PI (r =0.41; P < 0.0001). PKP-1+ and DP+ cells were correlated (0.32; P < 0.0001) and decreased from normal (81% versus 92.3%) to LSIL (53.1% versus 85.3%), to HSIL (46.4% versus 67.5%) and SCC (35.1% versus 35.9%). The Ki67+ PI was inversely correlated with DP (-0.20, P = 0.0014) and PKP-1 (-0.19, P = 0.015). Condylomata retained low CRBP-1 and high expression of PKP-1 and DP.

CONCLUSIONS

The gain of CRBP-1 and the loss of desmosomal proteins occur early in cervical carcinogenesis.

Increased concentrations of 3,4-didehydroretinol and retinoic acid-binding protein (CRABPII) in human squamous cell carcinoma and keratoacanthoma but not in basal cell carcinoma of the skin

Retinoids are biologic response modifiers that are present in normal skin and may possibly be perturbed in carcinogenesis. To examine this possibility in human skin, we analyzed vitamin A and cytosolic retinoid binding proteins (cellular retinol binding protein and cellular retinoic acid binding protein [CRABP]) in a total of 38 non-melanoma skin tumors and 25 healthy skin samples using high performance liquid chromatography, radioligand electrophoresis, and reverse transcriptase-polymerase chain reaction. The mean +/- SEM retinol concentration was normal in basal cell carcinoma (0.60 +/- 0.10 microM) and seborrheic keratosis (0.47 +/- 0.07 microM), but increased in keratoacanthoma (1.60 +/- 0.41 microM) and squamous cell carcinoma (1.17 +/- 0.28 microM) (p < 0.05 for both). Also, the concentrations of 3,4-didehydroretinol, a major vitamin A metabolite produced in human skin, were markedly elevated (6-7 times normal) in keratoacanthoma and squamous cell cancer. All types of tumors showed moderately increased levels of cellular retinol binding protein. In addition, keratoacanthoma and squamous cell cancer showed markedly increased levels (6-7 times normal) of CRABPII protein. Transcriptional activity of the CRABPII gene was demonstrated in both normal and neoplastic epidermis, but clear CRABPI mRNA expression was found only in basal cell carcinoma. The data indicate that characteristic perturbations of the vitamin A and retinoid binding protein levels occur in squamous cell-derived skin tumors, but whether these reflect intrinsic errors in retinoid metabolism or are secondary to abnormal cellular differentiation is unknown.

A relationship between retinol and cellular retinol-binding protein concentrations in human squamous cell carcinomas

The retinol and retinyl ester concentrations in human xenografted squamous cell carcinomas, with various concentrations of cellular retinol-binding protein (CRBP), were studied, as well as the in vivo uptake and esterification in these tumours of labelled retinol, presented as a complex with plasma RBP. The mean retinol concentration in the different tumours was in the range 3.7-6.2 nmol/g protein, and the mean CRBP concentration was between 16 and 69 nmol/g protein. There was a statistically significant correlation between the retinol and the CRBP concentrations in the same tumour (P less than 0.001; r = 0.622). Calculation of the maximal extent of retinol-saturation of CRBP showed low values (range: 9-26%). Retinyl palmitate, the predominant retinyl ester, comprised approx. 70% of the retinyl esters in the tumours. There was no correlation between the concentration of CRBP and that of retinyl palmitate. The uptake of [3H]retinol from intravenously injected retinol-RBP complex was similar in the four human squamous cell carcinomas studied, and not related to their CRBP concentration. 20% of the radioactivity in tumour specimens was lipid soluble, as compared to 96% in liver specimens, showing that in the former a higher fraction metabolised to polar compounds. Taken together, our results suggest that in these squamous carcinoma cells, factors other than cellular CRBP content are the major determinants of net cellular uptake and esterification of retinol. The cellular retinol concentration, on the other hand, appears proportional to CRBP content.