Date of Graduation

2006

Document Type

Dissertation/Thesis

Abstract

Breast cancer remains one of the most widespread cancers among women worldwide. Despite the existing evidence that implicates arachidonic acid (AA) metabolites, collectively called eicosanoids, in cancer onset and progression, little attention has been given to the enzymes, the cytosolic PLA2 (cPLA2), that usually provide free AA for eicosanoid biosynthesis. The present studies were undertaken to study the expression and regulation of the cPLA2-α, -β, -γ isoenzymes at the mRNA and protein levels, and of cyclooxygenase-2 (COX-2) and platelet 12-Lipoxygenase (12-LO) at mRNA level, the AA utilizing enzymes in MCF-7 cells. The present study shows that in MCF-7 cells the relative steady-state mRNA levels of cPLA 2β and cPLA2γ are higher basally than is the steady-state mRNA levels of cPLA2α and COX-2, levels that were at the detection limit. Arachidonic acid metabolism regulation by estrogen (E 2) and cytokines has been reported in other cell types. In the present study, we report that E2 treatment did not induce a change at the mRNA level of either COX-2 or cPLA2 isoenzymes (n=5). The steady-state mRNA levels of 12-LO, cPLA2α, cPLA2β, and cPLA2β splice variant containing intron 1 were not affected by the cytokines TNFα, TNFα/TGFβ, and IL-1β stimulation for 2, 6, 12, 24, and 48 hours. cPLA2γ mRNA levels were significantly increased following MCF-7 cells stimulation with TNFα for 6, 12, 24, and 48 h (p<0.05, n=4). Combination of TNFα with TGFβ elicited an increase of the cPLA2γ mRNA level following stimulation for 12 and 48 h (p<0.05, n=4). The increase in cPLA2γ mRNA levels was most evident following 2 h of IL-1β stimulation and the effect persisted over the examined times. COX-2 mRNA level showed a robust increase following TNFα, and IL-1β stimulation over the examined time (p<0.05, n=4). In MCF-7 cells, cPLA2β is expressed as 100 kDa protein, and cPLA2γ as 62 kDa microsomal protein as determined by immunodetection with isoform specific antibodies. cPLA 2β protein levels were insensitive to regulation by E2, TNFα, TNFα/TGFβ, or IL-1β following stimulation for 12h. cPLA2β protein levels increased when MCF-7 cells were maintained in 10% FBS as compared to 2% FBS. cPLA2γ protein level significantly increased following TNFα stimulation for 12 h (p<0.05, n=3). Biosynthesis of [1-14C]AA major metabolites by MCF-7 cells was almost undetectable. MCF-7 cells stimulation with E2, EGF, APAP, or IL-1β, or A23187 for 24 h did not modulate release or biosynthesis of radiolabeled AA major metabolites. The Ca2+ ionophore A23187 elicited an increased release of radiolabeled arachidonic acid. In conclusion, the results of this dissertation indicate that MCF-7 cells express cPLA 2β and cPLA2γ at levels that exceed cPLA 2α level. cPLA2γ expression increased by certain cytokines. MCF-7 cells exhibited a limited radiolabeled arachidonic acid metabolism that may be attributed to low expression of cPLA2α, usually the major enzyme responsible for eicosanoid biosynthesis. cPLA2β and cPLA2γ may participate in AA release and eicosanoid biosynthesis, and each may have different mechanisms of regulation or associated with different phases of eicosanoid biosynthesis, and perhaps unique signaling and cell type associated functions that remain undescribed.

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