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Estrogen Induction of Very Low Density Apolipoprotein II Synthesis, a Major Avian Liver Yolk Protein, Involves the Recruitment of Hepatocytes^*

CHIN-TARNG LIN, WILLIAM PALMER, JANG-YEN WU and LAWRENCE CHAN

Departments of Cell Biology and Medicine, Baylor College of Medicine Houston, Texas 77030

Address all correspondence and requests for reprints to: Dr. L. Chan, Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.

Abstract

The mechanism of steroid hormone action was studied in the cockerel liver. Very low density apolipoprotein II (apo-VLDL-II), a yolk protein, is a low molecular weight apolipoprqtein that is inducible by estrogen. The intracellular apo-VLDL-II messenger RNA (mRNA) concentration under various hormonal conditions was examined by a dot-blot assay. The concentration was very low in untreated cockerels (0.5 molecule per cell). It increased to 8,000 molecules per cell within 24 h of estrogen treatment and reached a maximum level of approximately 70,000 molecules per cell after 14 daily doses of estrogen. The distribution of hepatocytes harboring apo-VLDLII and its mRNA was studied by immunohistochemistry and by in situ nucleic acid hybridization to cloned [³H]apo-VLDL-II complementary DNA (cDNA). The number of cells containing the immunoreactive protein and the hybridizable mRNA increased from extremely low (0.3% and 0.27%, respectively) to substantial (11% and 10%, respectively) at 24 h after estrogen treatment and to extremely high (94% and 92%, respectively) in maximally treated animals. Our studies indicate that, in addition to enhanced transcription and stabilization of mRNA, the recruitment of liver cells previously not engaged in the synthesis of apo-VLDL-II is an important mechanism by which the hormone induces the hepatic production of this protein. The phenomenon of recruitment and the heterogeneity of the functional capacity of individual hepatocytes to respond to estrogen may be important to our understanding of estrogen action in the liver. (Endocrinology 118: 538–544, 1986)

Footnotes

^* This work was supported by NIH Grant HL-16512.

Present address: Department of Physiology, The Milton S. Hershey Medical Center, The Pennsylvania State University, Hershey, Pennsylvania 17033.

Received May 29, 1985.

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