Signal Transdaction in Hepatocyte Proliferation

我们最近报道了66%肝切除后再生肝细胞中[Ca^<2+>]_i的特征性振荡（Hepatology 21 ; 1395- 1404，1995）。为了进一步表征肝细胞增殖和分化过程中的[Ca^&lt;2+&gt;]_i反应，我们研究了苯肾上腺素诱导的（1）生理生长肝的原代培养肝细胞双联体和（2）用不耐热突变体SV 40大T抗原逆转录病毒转导条件永生化的大鼠肝细胞（SV 40 ^ T肝细胞）中的Ca^&lt;2+&gt;反应<ts>。在8周龄大鼠，[Ca^2+] i振荡在1周龄大鼠最多，此后[Ca^2+] i持续升高，提示[Ca^2+] i振荡可能调节生理性肝生长的细胞周期进程<ts>。所述多个非增生细胞（培养于39 ℃）在细胞外Ca^&lt;2 +&gt;存在的情况下，[Ca^&lt;2+&gt;]_i呈现非振荡性持续增加，在细胞外Ca ^&lt;2+&gt;不存在的情况下，其持续时间减弱。增殖的肝细胞（培养于33 ℃）在存在或不存在细胞外Ca^&lt;2 +&gt;的情况下，[Ca^&lt;2 +&gt;]_i都表现出短暂但非持续的增加<ts>。与来自生理生长的肝细胞中的发现相反，由于细胞核中存在SV 40 T抗原而进行有丝分裂的永生化肝细胞不显示[Ca^&lt;2+&gt;]_i振荡，表明这些细胞之间的增殖起始机制不同。

We recently reported characteristic [Ca^<2+>]_i oscillations in hepatocytes derived from livers regenerating in response to 66% hepatectomy (Hepatology 21 ; 1395-1404,1995). To further characterize [Ca^<2+>]_i responses during hepatocyte proliferation and differentiation, we investigated phenylephrine-evoked Ca^<2+> responses in (1) primary cultured hepatocyte doublets from physiologically growing liver, and (2) rat hepatocytes that were conditionally immortalized by retroviral transduction with a thermolabile mutant SV40 large T antigen (SV40^<ts>T hepatocytes).In hepatocytes obtained from 1-8 week-old rats, [Ca^<2+>]_i oscillations were most frequently observed in 1 week rats, and thereafter replaced by sustained increase in [Ca^<2+>]_i in 8 week rats, suggesting that [Ca^<2+>]_i oscillations might regulate cell-cycle progression in physiological liver growth.When SV40^<ts>T hepatocytes were stimulated with phenylephrine, the non-proliferating cells (cultured at 39ﾟC) presented a non-oscillatory sustained increase in [Ca^<2+>]_i in the presence of extracellular Ca^<2+>, the duration of which was attenuated in the absence of extracellular Ca^<2+>.In contrast, proliferating hepatocytes (cultured at 33ﾟC) showed a transient, but not sustained increase in [Ca^<2+>]_i both in the presence or absence of extracellular Ca^<2+>.In conclusion, SV40^<ts>T hepatocytes exhibit different Ca^<2+> responses during proliferation and differentiation.In contrast to the findings in hepatocytes from physiologically growing liver, the immortalized hepatocytes undergoing mitosis due to the presence of SV40 T antigen in their nuclei did not display [Ca^<2+>]_i oscillations, suggesting a difference in the mechanisms of proliferation initiation between these cells.