RESUMO
25-hydroxyvitamin D3 24-hydroxylase (CYP24A1), the catabolizing enzyme of the active vitamin D3, is often overexpressed in solid tumors. The unbalanced high levels of CYP24A1 seem to be a determinant of vitamin D resistance in tumors. Splice variants of CYP450 enzymes are common. Existence of CYP24A1 isoforms has been reported recently. We have investigated the presence of CYP24A1 splicing variants (SV) in human colon cancer cell lines and tissue samples. Using a set of primer combination we have screened the entire coding sequence of CYP24A1 and identified three splice variants in colon cancer cell lines. The presence of these SVs in human colon tissue samples showed a correlation with histological type of the tissue and gender of patients. The sequencing of the alternatively spliced fragments showed that two have lost the mitochondrial target domain, while the third lacks the heme-binding domain. All SVs retained their sterol binding domain. Translation of these variants would lead to a dysfunctional enzyme without catalytic activity that still binds its substrates therefore they might compete for substrate with the synthesizing and catabolizing enzymes of vitamin D.
Assuntos
Antineoplásicos/uso terapêutico , Neoplasias Colorretais/metabolismo , Esteroide Hidroxilases/biossíntese , Esteroide Hidroxilases/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Processamento Alternativo , Linhagem Celular Tumoral , Colo/metabolismo , Primers do DNA/genética , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Ligação Proteica , Esteróis/química , Vitamina D3 24-HidroxilaseRESUMO
Epidemiologic studies suggest that alcohol may be an inducing factor in human colon tumorigenesis. As colon cells are frequently under autocrine control by growth factors, involvement of the EGFR pathway in alcohol-related colon tumor progression was investigated in the human colon adenocarcinoma-derived cell line Caco-2 which shows EGFR distribution mainly in basolateral cell membranes. EGF treatment results in almost complete downregulation of the basolateral receptor. Low concentrations of ethanol (0.22 mM, 0.1%) however, lead to significantly increased EGFR mRNA and protein expression and a raised mitotic rate mainly in basolaterally treated cells. Alcohol-induced overexpression of EGFR is paralleled by increased cyclin D1 expression. This suggests a possible mechanism for low blood levels of alcohol to stimulate in vivo proliferation of colonocytes by elevating transcription of a growth factor receptor as well as by modifying expression of a cell cycle regulator.
Assuntos
Adenocarcinoma/genética , Neoplasias do Colo/genética , Receptores ErbB/genética , Etanol/farmacologia , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Adenocarcinoma/patologia , Células CACO-2 , Divisão Celular/efeitos dos fármacos , Neoplasias do Colo/patologia , Ciclina D1/genética , Receptores ErbB/metabolismo , Receptores ErbB/fisiologia , Humanos , RNA Mensageiro/genéticaRESUMO
The human colon adenocarcinoma-derived cell line Caco-2 was used as a model system to study the interaction of epidermal growth factors (EGF) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in control of colorectal cancer cell growth. The mitogenic stimulus of EGF was rapidly transduced via apical and basal membrane receptors alike into elevation of c-myc expression, causing a shift of Caco-2 cells from the G0/G1 into the S phase of the cell cycle. The stimulatory effect of EGF on cell division was effectively counteracted by 1,25(OH)2D3: the presence of the steroid hormone prevents the negative effect of EGF on vitamin D receptor abundance and concurrently minimises ligand-occupied EGF receptor numbers on both sides of Caco-2 cell monolayers. Our data suggest that EGF and 1,25-(OH)2D3 actions on mutual receptor levels represent a specific feature of the potent antimitogenic effect of the steroid hormone on colon cancer cells.
