title: Calreticulin is a fine tuning molecule in epibrassinolide-induced apoptosis through activating endoplasmic reticulum stress in colon cancer cells.
abstract: Epibrassinolide (EBR), a member of brassinostreoids plant hormones with cell proliferation promoting role in plants, is a natural polyhydroxysteroid with structural similarity to steroid hormones of vertebrates. EBR has antiproliferative and apoptosis-inducing effect in various cancer cells. Although EBR has been shown to affect survival and mitochondria-mediated apoptosis pathways in a p53-independent manner, the exact molecular targets of EBR are still under investigation. Our recent SILAC (Stable Isotope Labeling by Amino Acids in Cell Culture) data showed that the most significantly altered protein after EBR treatment was calreticulin (CALR). CALR, a chaperone localized in endoplasmic reticulum (ER) lumen, plays role in protein folding and buffering Ca2+ions. The alteration of CALR may cause ER stress and unfolded protein response correspondingly the induction of apoptosis. Unfolded proteins are conducted to 26S proteasomal degradation following ubiquitination. Our study revealed that EBR treatment caused ER stress and UPR by altering CALR expression causing caspase-dependent apoptosis in HCT 116, HT29, DLD-1, and SW480 colon cancer cells. Furthermore, 48 h EBR treatment did not caused UPR in Fetal Human Colon cells (FHC) and Mouse Embryonic Fibroblast cells (MEF). In addition our findings showed that HCT 116 colon cancer cells lacking Bax and Puma expression still undergo UPR and related apoptosis. CALR silencing and rapamycin co-treatment prevented EBR-induced UPR and apoptosis, whereas 26S proteasome inhibition further increased the effect of EBR in colon cancer cells. All these findings showed that EBR is an ER stress and apoptotic inducer in colon cancer cells without affecting non-malignant cells.
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Pinar
authors.initials: P
authors.lastname: Obakan-Yerlikaya
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Elif Damla
authors.initials: ED
authors.lastname: Arisan
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Ajda
authors.initials: A
authors.lastname: Coker-Gurkan
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Kaan
authors.initials: K
authors.lastname: Adacan
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Utku
authors.initials: U
authors.lastname: Ozbey
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Berna
authors.initials: B
authors.lastname: Somuncu
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Didem
authors.initials: D
authors.lastname: Baran
authors.affiliation: Department of Molecular Biology and Genetics, Istanbul Kultur University, Ataköy Campus, Istanbul, Turkey.
authors.forename: Narcin
authors.initials: N
authors.lastname: Palavan-Unsal
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D060406:Brassinosteroids / Q000737:chemistry* / Q000494:pharmacology*; D037282:Calreticulin / Q000378:metabolism*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D003106:Colon / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D045325:HCT116 Cells; D006801:Humans; D051379:Mice; D010937:Plant Growth Regulators / Q000737:chemistry / Q000494:pharmacology; D056811:Unfolded Protein Response / Q000187:drug effects
chemical_list: D000970:Antineoplastic Agents; D060406:Brassinosteroids; C576483:CALR protein, human; D037282:Calreticulin; D010937:Plant Growth Regulators
keywords: colon cancer; endoplasmic reticulum stress; epibrassinolide; unfolded protein response