Tavtigian S V, Zabludoff S D, Wold B J
Myriad Genetics, Salt Lake City, Utah 84108.
Mol Biol Cell. 1994 Mar;5(3):375-88. doi: 10.1091/mbc.5.3.375.
The emergence of cells from a quiescent G0 arrested state into the cell cycle is a multistep process that begins with the immediate early response to mitogens and extends into a specialized G1 phase. Many immediate early serum response genes including c-fos, c-myc, and c-jun are transcriptional regulators. To understand their roles in regulating cell cycle entry and progression, the identities of their regulatory targets must be determined. In this work we have cloned cDNA copies of messenger RNAs that are either up- or down-regulated at a mid-G1 point in the serum response (midserum-response [mid-SR]). The mid-SR panel is expected to include both direct and indirect targets of immediate early regulators. This expectation was confirmed by the identification of several transcriptional targets of conditional c-myc activity. In terms of cellular function, the mid-SR class is also expected to include execution genes needed for progression through G1 and into S-phase. DNA sequence data showed that the mid-SR panel included several genes already known to be involved in cell cycle progression or growth transformation, suggesting that previously unknown cDNAs in the same group are good candidates for other G1 execution functions. In functional assays of G0-->S-phase progression, c-myc expression can bypass the requirement for serum mitogens and drive a large fraction of G0 arrested cells through G1 into S-phase. However, beyond this general similarity, little is known about the relation of a serum-driven progression to a myc-driven progression. Using the mid-SR collection as molecular reporters, we found that the myc driven G1 differs qualitatively from the serum driven case. Instead of simply activating a subset of serum response genes, as might be expected, myc regulated some genes inversely relative to serum stimulation. This suggests that a myc driven progression from G0 may have novel properties with implications for its action in oncogenesis.
细胞从静止的G0期阻滞状态进入细胞周期是一个多步骤过程，始于对有丝分裂原的即时早期反应，并延伸至特定的G1期。许多即时早期血清反应基因，包括c-fos、c-myc和c-jun，都是转录调节因子。为了解它们在调节细胞周期进入和进程中的作用，必须确定其调节靶点的身份。在这项研究中，我们克隆了在血清反应的G1中期（中期血清反应[mid-SR]）上调或下调的信使RNA的cDNA拷贝。中期血清反应基因库预计包括即时早期调节因子的直接和间接靶点。通过鉴定条件性c-myc活性的几个转录靶点，证实了这一预期。就细胞功能而言，中期血清反应基因类别预计还包括G1期进程及进入S期所需的执行基因。DNA序列数据表明，中期血清反应基因库包括几个已知参与细胞周期进程或生长转化的基因，这表明同一组中先前未知的cDNA是其他G1执行功能的良好候选基因。在G0期到S期进程的功能测定中，c-myc表达可以绕过对血清有丝分裂原的需求，并驱动大部分G0期阻滞细胞通过G1期进入S期。然而，除了这种普遍的相似性之外，关于血清驱动进程与myc驱动进程之间的关系知之甚少。利用中期血清反应基因库作为分子报告基因，我们发现myc驱动的G1期与血清驱动的情况在质量上有所不同。与预期的简单激活一部分血清反应基因不同，myc对一些基因的调节与血清刺激呈负相关。这表明从G0期开始的myc驱动进程可能具有新特性，对其在肿瘤发生中的作用具有重要意义。
