Doxorubicin (DOX)-induced cardiomyopathy has been found to be associated with impaired Ca(2+) handling in the sarcoplasmic reticulum (SR), leading to reduced cardiac function. We have recently demonstrated that expression of mRNA encoding sarco(endo)plasmic reticulum Ca(2+)-ATPase 2 (SERCA2), a major Ca(2+) transport protein in SR, is markedly decreased in DOX-treated hearts. To extend this observation, we have dissected the molecular mechanisms by which DOX downregulates SERCA2 gene transcription. Using cultured rat neonatal cardiac myocytes, we found that the antioxidant N-acetylcysteine blocked the DOX-induced decrease in SERCA2 mRNA levels, as well as the DOX-induced increase in H(2)O(2) concentration; thus, H(2)O(2) is an intracellular mediator of DOX activity. Using a luciferase reporter assay, we found that the sequence from -284 to -72 bp in the 5' flanking region of the SERCA2 gene has a DOX-responsive element. Although several transcription factors have putative binding motifs in this region of the SERCA2 gene, only the expression of Egr-1 mRNA and the binding of Egr-1 protein to the 5' regulatory sequence of SERCA2 gene increased markedly after DOX administration. We also found that overexpression of Egr-1 was associated with a significant reduction in SERCA2 gene transcription. In addition, Egr-1 antisense oligonucleotides blocked the DOX-induced reduction in SERCA2 mRNA, suggesting that Egr-1 is a transcriptional inhibitor of the SERCA2 gene in DOX-induced cardiomyopathy. We observed activation of 3 mitogen-activated protein kinases (MAPKs), p44/42 MAPK, p38 MAPK, and stress-activated MAPK/Jun N-terminal kinase, by DOX, but only a specific inhibitor of the p44/42 MAPK kinase suppressed the effects of DOX on Egr-1 and SERCA2 mRNA expression. These findings indicate that reactive oxygen intermediates, the transcription factor Egr-1, and p44/42 MAPK are critical elements in the transcriptional regulation of the SERCA2 gene in response to DOX.

Objective

We report our experience with a patient whose mediastinal lymphadenopathy resolved after resection of a cardiac myxoma that secreted interleukin-6 (IL-6). The patient was a 68-year-old female who complained of nocturnal chest discomfort related to congestive heart failure. An echocardiogram demonstrated a large left atrial mass. A computed tomogram showed not only the left atrial mass but multiple enlarged mediastinal lymph nodes. The serum IL-6 level was markedly elevated at 13.7 pg/ml. After resection of the cardiac myxoma, serum IL-6 returned to the normal range. A repeat computed tomogram showed no mediastinal lymphadenopathy. We believe that overproduction of IL-6 by the cardiac myxoma was the cause of the mediastinal lymphadenopathy.

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