Physiological significance of proHB-EGF ectodomain shedding in epideimal development

HB-EGF是EGF家族的一员。为了检查HB-EGF在体内的作用，我们产生了HE-EGF敲除小鼠HB（<del/del>）。与条件性ErbB 2敲除小鼠类似，HB^<del/del>小鼠发展出严重的心力衰竭，伴有扩张的心室腔。HB^<del/del>小鼠也发展出增大的心脏瓣膜，类似于EGFR敲除小鼠。在HB^<del/del>心脏中，ErbB 2和ErbB 4的组成型酪氨酸磷酸化显著降低。（2）HB-EGF首先以膜锚定形式（proHB-EGF）合成，其可溶性形式（sHB-EGF）由proHB-EGF的胞外域脱落释放。为了研究proHB-EGF在体内加工的意义，我们通过靶向基因置换产生突变小鼠，表达分子的不可切割形式（HB^<uc>）或跨膜结构域截短形式（HB^&lt;Δtm&gt;）。HB^&lt;uc/uc&gt;小鼠出现严重心力衰竭， ...更多信息 心脏瓣膜增大，表型与proHB-EGF-null小鼠相似。HB^&lt;Δtm&gt;小鼠的皮肤和心脏均出现严重的增生，提示proHB-EGF的胞外区脱落是HB-EGF在体内发挥功能所必需的，这一过程需要严格控制。3）HB^&lt;del/del&gt;小鼠表皮发育过程未见异常。因此，我们研究了HE-EGF在再上皮化中的作用。HB-EGF在成人表皮中的表达在稳态时几乎没有检测到，但在全层创伤和局部用维甲酸（tRA）处理后强烈诱导。以选择性阻断基底层角质形成细胞HB-EGF表达的突变小鼠（HB^&lt;del/del&gt;-K5-Cre）、HB^&lt;uc/uc&gt;小鼠和正常HB-EGF cDNA基因敲入小鼠（HB^&lt;lox/lox&gt;）为实验对照，观察tRA诱导角质形成细胞增殖和伤口愈合的情况。在HB^&lt;del/del&gt;-K5-Cre小鼠和HBuc/uc小鼠中，与HBlox/lox小鼠相比，tRA诱导的表皮过度增殖和伤口愈合活性均降低。提示HB-EGF的诱导及其胞外区的脱落是体内再上皮化过程中的一个重要环节。少

1)HB-EGF is a member of the EGF family of giowth factors. To examine the role of HB-EGF in viva, we generated HE-EGF-knockout mice HB^<del/del>). HB^<del/del> mice developed severe heart failure with dilated ventricular chambers, similarly to conditional ErbB2 knockout mice. HB^<del/del> mice developed also enlarged cardiac valves, similarly to EGFR knockout mice. Constitulive tyrosine phosphorylation of both ErbB2 and ErbB4 was significantly reduced in HB^<del/del> hearts. These indicated that HB-EGFactivalion of ErbB is essential for normal heartfunclion.2)HB-EGF is first synthesized as a membrane-anchored form (proHB-EGF), and its soluble form (sHB-EGF) is released by ectodomain shedding fiom proHB-EGF. To examine the significance of proHB-EGF processing in vivo, we generated mutant mice by targeted gene replacement, xpressing either an uncleavable form (HB^<uc>) or a transmembrane domain-truncated form (HB^<Δtm>) of the molecule. HB^<uc/uc> mice developed severe heart failure and e … More nlarged heart valves, phenotypes similar to those in proHB-EGF-null mice. On the other hand, mice canying HB^<Δtm> exhibited severe hyperplasia in both skin and heart These results indicate that ectodomain shedding of proHB-EGF is essential for HB-EGF function in viva, and that this piocess requires strict control.3)HB^<del/del> mice did not show any abnormalities in developmental piocess of epidermis. Thus, we investigated the role of HE-EGF in re-epithelization. HB-EGF expression in adult epidermis was hardly detected at the steady state, but it was strongly induced after full-thickness wounding and topical treatment with retinoic acid (tRA). The level of hyperprolifemtion of keratinocytes induced by tRA-ireatinent and that of wound healing were estimated among the mutant mice selectively ablated HB-EGF expression in basal keratinocytes (HB^<del/del>-K5-Cre),HB^<uc/uc> mice and normal HB-EGF cDNA knock-in mice (HB^<lox/iox>) as an experimenrtal control. In HB^<del/del>-K5-Cre mice and in HBuc/uc mice, both tRA-induced epidermal hyperproliferation and wound healing activity was reduced compared with HBlox/lox mice. These indicated that the induction of HB-EGF and its ectodomain shedding is an important event in the re-epithelization in vivo. Less