Hypomethylation of LINE-1 retrotransposon in breast cancer cells exposed to pesticides. Role of TGF-β1 pathway

NOELIA MIRET; GABRIELA ALTAMIRANO; DANIEL ZAPPIA; AYELÉN GÓMEZ; CAROLINA PONTILLO; LORENA ZÁRATE; MARIANELA LASAGNA; CLAUDIA COCCA; FEDERICO MONCZOR; LAURA KASS; ANDREA RANDI

Mar del Plata

Congreso; Reunión Anual de Sociedades de Biociencias; 2019

Sociedad Argentina de Investigación Clínica, Sociedad Argentina de Farmacología Exoperimental, Sociedad Argentina de Biología y Sociedad Argentina de Protozoología

Long interspersed nuclear element 1 (LINE-1) isthe most common non-LTR retrotransposon in the human genome and comprises 17%of the genome. Reactivation of LINE-1 has been linked to breast cancerprogression and metastasis. Strong ligands of aryl hydrocarbon receptor (AhR) activateLINE-1 through the transforming growth factor-β1 (TGF-β1) pathway in humanliver cancer cells. We have observed that environmental doses of two weak AhR ligands:the organochlorine pesticide hexachlorobenzene (HCB, 0.005 μM) and the organophosphatechlorpyrifos (CPF, 0.5 μM) activate the TGF-β1 signaling and enhance LINE-1mRNA expression in the human breast cancer cell line MDA-MB-231. Our aim was toinvestigate the role of the TGF-β1 signaling in the mechanism of action and ifthe pesticides induce epigenetic changes.To study the involvement of the TGF-β1signaling on LINE-1 expression, cells were exposed to HCB or CPF in thepresence of the TGF-β1 receptor I inhibitor (SB431542, 2 µM). qPCR results showed that the enhancement exerted by the pesticides wasprevented by the treatment with the inhibitor (p<0.05). Considering that LINE-1expression is regulated by methylation of its internal promoter, MDA-MB-231cells were exposed to HCB or CPF and the methylation status of the LINE-1 5´-UTRwas determined. Six sites (+38, +103, +167, +234, +306, +373) were analyzed by acombination of single digestions with methylation-sensitive restriction enzymesand qPCR. We found that the methylation was reduced by HCB at the sites +38,+103 and +167 (p<0.05) and by CPF at the sites +38 and +103 (p<0.05).In conclusion, HCB and CPF induce thedemethylation of LINE-1 and enhance mRNA expression through TGF-β1 pathway. Ourfindings support previous investigations showing that methylation of the firstsites in 5´-UTR are essential for the LINE-1 transcriptional regulation. Finally,environmental doses of pesticides promote epigenetic changes that couldincrease human breast cancer risk.<!-- /* Font Definitions */ @font-face{font-family:"Cambria Math";panose-1:2 4 5 3 5 4 6 3 2 4;mso-font-charset:0;mso-generic-font-family:roman;mso-font-pitch:variable;mso-font-signature:-536870145 1107305727 0 0 415 0;}@font-face{font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;mso-font-charset:0;mso-generic-font-family:swiss;mso-font-pitch:variable;mso-font-signature:-536859905 -1073732485 9 0 511 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal{mso-style-unhide:no;mso-style-qformat:yes;mso-style-parent:"";margin-top:0cm;margin-right:0cm;margin-bottom:8.0pt;margin-left:0cm;line-height:107%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;mso-fareast-language:EN-US;}.MsoChpDefault{mso-style-type:export-only;mso-default-props:yes;font-size:11.0pt;mso-ansi-font-size:11.0pt;mso-bidi-font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;mso-fareast-language:EN-US;}.MsoPapDefault{mso-style-type:export-only;margin-bottom:8.0pt;line-height:107%;}size:612.0pt 792.0pt;margin:70.85pt 3.0cm 70.85pt 3.0cm;mso-header-margin:35.4pt;mso-footer-margin:35.4pt;mso-paper-source:0;}div.WordSection1{page:WordSection1;}