Yuan X, Zheng X, Lu D, Rubin D C, Pung C Y, Sadler J E
Howard Hughes Medical Institute, Department of Medicine, Barnes-Jewish Hospital, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Am J Physiol. 1998 Feb;274(2):G342-9. doi: 10.1152/ajpgi.1998.274.2.G342.
Enterokinase (enteropeptidase) is expressed only in proximal small intestine, where it initiates digestive enzyme activation by converting trypsinogen into trypsin. To investigate this restricted expression pattern, mouse enterokinase cDNA was cloned, and the distribution of enterokinase mRNA and enzymatic activity were determined in adult mice and during gestation. Analysis of enterokinase sequences showed that a mucinlike domain near the NH2 terminus is composed of repeated approximately 15-amino acid Ser/Thr-rich motifs. By Northern blotting and trypsinogen activation assays, enterokinase mRNA and enzymatic activity were undetectable in stomach, abundant in duodenum, and decreased distally until they were undetectable in midjejunum, ileum, and colon. By in situ mRNA hybridization, enterokinase mRNA was localized to the enterocytes throughout the villus. Expression was not observed in goblet cells, Paneth cells, or Brunner's glands. Enterokinase mRNA and enzymatic activity were not detected in the duodenum of fetal mice but were easily detected in the duodenum on postnatal days 2-6. Both enterokinase mRNA and enzymatic activity decreased to very low levels after day 7 but increased after weaning and reached a high level characteristic of adult life by day 60. Therefore, in mice, duodenal enterocytes are the major type of cells expressing enterokinase, which appears to be regulated at the level of mRNA abundance.
肠激酶（肠肽酶）仅在近端小肠表达，在那里它通过将胰蛋白酶原转化为胰蛋白酶来启动消化酶的激活。为了研究这种受限的表达模式，克隆了小鼠肠激酶cDNA，并在成年小鼠和妊娠期测定了肠激酶mRNA的分布和酶活性。对肠激酶序列的分析表明，靠近NH2末端的粘蛋白样结构域由重复的约15个氨基酸的富含丝氨酸/苏氨酸的基序组成。通过Northern印迹和胰蛋白酶原激活试验，在胃中未检测到肠激酶mRNA和酶活性，在十二指肠中丰富，向远端逐渐减少，直到在空肠中部、回肠和结肠中无法检测到。通过原位mRNA杂交，肠激酶mRNA定位于整个绒毛的肠上皮细胞。在杯状细胞、潘氏细胞或十二指肠腺中未观察到表达。在胎鼠十二指肠中未检测到肠激酶mRNA和酶活性，但在出生后第2 - 6天的十二指肠中很容易检测到。肠激酶mRNA和酶活性在第7天后均降至极低水平，但在断奶后增加，并在第60天达到成年期的高水平特征。因此，在小鼠中，十二指肠肠上皮细胞是表达肠激酶的主要细胞类型，其表达似乎在mRNA丰度水平上受到调节。
