Insulin-induced activation of phosphoinositide 3-kinase in Fao cells

Summary Phosphoinositide 3-kinase (PI3-kinase) plays a crucial role in insulin signal transduction. We studied the molecular mechanism of the insulin-induced activation of PI3-kinase in rat hepatoma Fao cells using an antibody against the 110-kDa catalytic subunit (p110) and two against the 85-kDa regulatory subunit (p85). PI3-kinase activity increased 1.6-fold in anti-p85 immunoprecipitates after insulin stimulation, whereas it did not increase when cell lysates were first immunoprecipitated with anti-phosphotyrosine or anti-insulin receptor substrate-1 (IRS-1), then with anti-p85, suggesting that the PI3-kinase which associates with tyrosyl phosphoproteins including IRS-1 is responsible for the increase in kinase activity. The activated PI3-kinase molecules constituted 4–6% of the total PI3-kinase, and their specific activity was 11–14 times higher than that of the basal state. Anti-p110 recognized the catalytically active form of p110, and immunoprecipitated p110 only after exposure to insulin. Hence, the epitope of anti-p110, P200-C215, seems to be included in the portion of p110, the conformation of which is changed by insulin stimulation. We conclude that, in response to insulin stimulation, only a small fraction of p85 in the PI3-kinase pool associates with tyrosyl phosphoproteins including IRS-1, and that the specific activity of p110 is increased presumably through a conformational change including the P200-C215 region.Abbreviations PI3-kinase Phosphoinositide 3-kinase - p85 85-kDa subunit of PI3-kinase - p110 110-kDa subunit of PI3-kinase - IRS-1 insulin receptor substrate-1 - SH2 src homology 2 - SH3 src homology 3 - BCR breakpoint cluster region - PMSF phenylmethylsulphonyl fluoride - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid - PIP phosphatidylinositol phosphate - TLC thin layer chromatography - IP (in figures) immunoprecipitation with the indicated antibody - TBS Tris-buffered saline     

Pedunculated gastric carcinoma demonstrating a gastric foveolar phenotype

We report a case of gastric cancer complicated with very well differentiated adenocarcinoma containing signet ring cells. An endoscopic examination revealed a pedunculated polyp in the fornix of the stomach. A surgical operation was performed and the pathological findings showed very well differentiated adenocarcinoma mimicking gastric foveolae with a poorly differentiated component containing signet ring cells. This is the first case of pedunculated gastric cancer complicated with very well differentiated adenocarcinoma containing signet ring cells and also demonstrating a gastric foveolar phenotype.     

E-cadherin molecular expresion in the diffuse and intestinal types of gastric adenocarcinoma. A report from Lima, Peru]

OBJECTIVE: Signet ring carcinoma of the stomach is well known to be more aggressive and infiltrating than adenocarcinoma. Different studies have proposed that signet ring cell carcinoma would be more infiltrating because of the loss of E-cadherin expression, this cadherin is a class of protein cell membrane protein which plays an important role in cell-adhesion. METHODS: We carried out a transversal comparative study, in order to measure the E-cadherin expression in 10 cases of signet ring cell and in 10 cases of adenocarcinoma, with help of immunohistochemistry. RESULTS: We found a bigger expression of E-cadherin in adenocarcinomas (100%) than signet ring cell carcinoma (40%), this difference was significative using Fisher test (p = 0,011). The loss of E-cadherin would explain the bigger infiltrating capacity in comparison to adenocarcinoma.     

Coexistence of multifocal gastric adenocarcinoma with signet-ring cell morphology and a gastrointestinal stromal tumour in a stomach with hp-associated gastritis

A 79-year-old man was admitted because of anemia during marcumar therapy with suspected bleeding in the gastrointestinal tract. Endoscopy revealed a large mutifocal poorly differentiated gastric signet ring cell adenocarcinoma. After staging by the usual oesophagogastroduodenoscopic method, a total D 2 gastrectomy was performed. In the pathological resection specimen of the stomach, a multifocal poorly differentiated signet ring cell adenocarcinoma, infiltrating the submucosa (so called early cancer of sm-type) and an incidental gastroinstinal stromal tumour, 0.8 cm in diameter, was diagnosed. This is the first case report of the synchronous occurrence of a multifocal poorly differentiated gastric adenocarcinoma with signet-ring cell morphology (diffuse type according to the Lauren classification) and a GIST incidentally within a stomach with Hp-associated gastritis.     

Activation of phosphatidylinositol 3-kinase by epidermal growth factor, basic fibroblast growth factor, and nerve growth factor in PC12 pheochromocytoma cells.

Epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and nerve growth factor (NGF), which stimulate the phosphorylation of proteins on tyrosine in PC12 cells, initiate these modifications through ligand-specific cell surface receptors that contain the causative tyrosine kinases. One apparent substrate for these enzymes is phosphatidylinositol 3-kinase (PI 3-kinase), an enzyme that phosphorylates the D-3 position of the inositol ring and associates with several protein tyrosine kinases, as indicated by the fact that it is immunoprecipitated from EGF-, bFGF-, and NGF-stimulated PC12 cells by an anti-phosphotyrosine antibody. All three growth factors increase immunoprecipitable PI 3-kinase activity after 2 min of addition at concentrations able to stimulate either mitogenic or neurotrophic responses in PC12 cells. The level of stimulation of PI 3-kinase activity by EGF, bFGF, and NGF is 15- to 20-fold, 2- to 3-fold, and 8- to 10-fold, respectively. Moreover, tyrosine phosphorylation of PI 3-kinase was detected in EGF-, bFGF-, and NGF-stimulated PC12 cells, and the amount of the phosphorylation correlated with the level of stimulation of enzyme activity. In contrast, phosphatidylinositol 4-kinase, which produces the inositol phospholipids cleaved by phospholipase C-gamma to yield diacylglycerol and inositol-1,4,5-trisphosphate, is not affected by these growth factors. The pattern of stimulation of PI 3-kinase does not correlate with the induction of neurite outgrowth but rather with the mitotic responses, suggesting that PI 3-kinase and its products may be more important for signaling in cell division than in trophic processes. However, the levels of phosphatidylinositol 3-phosphate do not coincide with the stimulation of [3H]thymidine incorporation by these growth factors, rendering its role in mitotic functions, at least in PC12 cells, also uncertain.     

Cathepsins D and E in normal, metaplastic, dysplastic, and carcinomatous gastric tissue: an immunohistochemical study.

Immunohistochemical distributions of cathepsins D and E were determined in normal mucosa, metaplastic, dysplastic, and cancerous lesions of the human stomach. Cathepsins D and E were localised in the foveolar epithelium and parietal cells of the normal gastric mucosa, but their intracytoplasmic distributions were different - cathepsin E distribution was even and diffuse in the cytoplasm while cathepsin D was found in coarse intracytoplasmic granules. Chronic inflammation and ulcer did not influence the distribution of these enzymes. No positive staining was obtained in the incomplete type of intestinal metaplasia, dysplasia, and well differentiated adenocarcinoma. Tumour cells of signet ring cell carcinoma and poorly differentiated adenocarcinoma cells, however, gave strong and diffuse stainings for cathepsins D and E in the cytoplasm. The results suggest that the distribution of cathepsins D and E is related to each specialised function of the foveolar epithelium and the parietal cells, and that their disappearance is associated with development of well differentiated adenocarcinoma from intestinal metaplasia.     

Multiple early gastric cancer with gastritis cystica profunda showing various histological types

We report a case of multiple early gastric cancer showing varied histological types associated with gastritis cystica profunda (GCP). A 61-year-old man who had early gastric cancer associated with GCP underwent a distal gastrectomy with lymphadenectomy. Histological examination showed various histological types of cancer -well differentiated, moderately differentiated, poorly differentiated adenocarcinoma, mucinous adenocarcinoma and signet ring cell carcinoma- that had developed independently in the mucosal and submucosal layers of the resected specimen. Furthermore, multiple cysts with a single layer of columnar epithelium were present in the submucosa around the cancerous lesions. However, no neoplastic changes were found in those epithelial cells. Helicobacter pylori was detected in the residual stomach 3 months after surgery. Although the mechanism of the relationship between gastric carcinoma and GCPs is obscure, we speculate that repeated erosion and regeneration induced by chronic inflammation causes multicentric carcinogenesis as well as an aberration of the gastric glands. GCPs may be a risk factor for multiple gastric cancer.     

早期胃癌淋巴结转移规律及内镜切除指征的探讨

目的探讨不同组织学类型早期胃癌的淋巴结转移情况及内镜下治疗的可行性。方法回顾性分析524例行胃癌根治术治疗并经病理确诊的早期胃癌患者的病例资料,比较不同组织学类型早期胃癌的临床病理特征并对其与淋巴结转移的相关性进行单因素及多因素分析。结果印戒细胞癌与分化型腺癌、低分化腺癌相比,在肿瘤大小（P值分别为0．048和0．023）和浸润深度（P值均为0．000）方面差异均有统计学意义,其淋巴结转移率（9．7％,11／113）明显低于低分化型腺癌（22．2％,20／90）,差异有统计学意义（P=0．018）,但与分化型腺癌（13．t％,42／321）比较差异无统计学意义（P=0．406）。单因素分析显示肿瘤大小（P=0．007）、浸润深度（P=0．000）、组织学类型（P=0．030）、淋巴管肿瘤浸润（P=0．000）和有无溃疡（P=0．002）与淋巴结转移显著相关;多因素分析结果显示浸润深度（P=0．007）、肿瘤大小（P=0．010）、组织学分型（P=0．000）和淋巴管肿瘤浸润（P=0．000）为淋巴结转移的独立危险因素。联合上述4个独立危险因素分析显示肿瘤直径小于2cm且无淋巴管肿瘤浸润的印戒细胞型黏膜内癌未见淋巴结转移。结论印戒细胞型早期胃癌的临床病理特征与分化型和低分化型早期腺癌存在差异,直径小于2cm且无淋巴管肿瘤浸润的印戒细胞型黏膜内癌患者可行内镜切除术。     

Phorbol ester treatment inhibits phosphatidylinositol 3-kinase activation by, and association with, CD28, a T-lymphocyte surface receptor.

CD28 is a costimulatory receptor found on the surface of most T lymphocytes. Engagement of CD28 induces interleukin 2 (IL-2) production and cell proliferation when combined with an additional signal such as treatment with phorbol ester, an activator of protein kinase C. Recent studies have established that after CD28 ligation, the cytoplasmic domain of CD28 can bind to the 85-kDa subunit of phosphatidylinositol 3-kinase (PI3 kinase). There is a concomitant increase in PI3 lipid kinase activity that may be important in CD28 signaling. Despite the requirement of phorbol 12-myristate 13-acetate (PMA) for effector function, we have found, however, that treatment of Jurkat T cells with the phorbol ester PMA dramatically inhibits (i) the association of PI3 kinase with CD28, (ii) the ability of p85 PI3 kinase to be immunoprecipitated by anti-phosphotyrosine antibodies, and (iii) the induction of PI3 kinase activity after stimulation of the cells with the anti-CD28 monoclonal antibody 9.3. These changes occur within minutes of PMA treatment and are persistent. In addition, we have found that wortmannin, a potent inhibitor of PI3 kinase, does not interfere with the induction of IL-2 after stimulation of Jurkat T cells with anti-CD28 monoclonal antibody and PMA. We conclude that PI3 kinase activity may not be required for CD28-dependent IL-2 production from Jurkat T cells in the presence of PMA.     

Expression of estrogen receptor and estrogen receptor messenger RNA in gastric carcinoma tissues

AIM: To study estrogen receptor (ER) and estrogen receptor messenger RNA (ERmRNA) expression in gastric carcinoma tissues and to investigate their association with the pathologic types of gastric carcinoma.METHODS: The expression of ER and ERmRNA in gastric carcinoma tissues (15 males and 15 females, 42-70 years old) was detected by immunohistochemistry and in situ hybridization, respectively.RESULTS: The positive rate of ER (immunohistochemistry)was 33.3% in males and 46.7% in females. In Borrmann Ⅳ gastric carcinoma ER positive rate was greater than that in other pathologic types, and in poorly differentiated adenocarcinoma and signet ring cell carcinoma the positive rates were greater than those in other histological types of both males and females (P＜0.05). The ER was more highly expressed in diffused gastric carcinoma than in non-diffused gastric carcinoma (P＜0.05). The ER positive rate was also related to regional lymph nodes metastases (P＜0.05), and was significantly higher in females above 55 years old, and higher in males under 55 years old (P＜0.05). The ERmRNA (in situ hybridization) positive rate was 73.3% in males and 86.7% in females. The ERmRNA positive rates were almost the same in Borrmann Ⅰ, Ⅱ, Ⅲ and Ⅳ gastric carcinoma (P＞0.05). ERmRNA was expressed in all tubular adenocarcinoma, poorly differentiated adenocarcinoma and signet ring cell carcinoma (P＜0.05). The ERmRNA positive rate was related to both regional lymph nodes metastases and gastric carcinoma growth patterns, and was higher in both sexes above 55 years old but without statistical significance (P＞0.05). The positive rate of ERmRNA expression by in situ hybridization was higher than that of ER expression by immunohistochemistry (P＜0.05).CONCLUSION: ERmRNA expression is related to the pathological behaviors of gastric carcinoma, which might help to predict the prognosis and predict the effectiveness of endocrine therapy for gastric carcinoma.     

Newly established human pancreatic carcinoma cell lines and their lectin binding properties

Summary Two human pancreatic carcinoma cell lines, designated HuP-T3 and HuP-T4, were established from the ascites of pancreatic cancer patients with carcinomatous peritonitis. The cell lines were grown in monolayer cultures and had population doubling times of 38.6 and 37.1 h, respectively. HuP-T4 secreted large amounts of CEA and CA19-9 into the medium, and HuP-T3 produced a small amount of CEA, but no CA19-9. Both cell lines showed tumorigenicity in nude mice. Histologically, the HuP-T3-derived tumor was poorly differentiated adenocarcinoma, and the HuP-T4-derived tumor was well differentiated papilotubular adenocarcinoma. In lectin histochemistry at both light and electron microscopic levels, the most striking difference between the lectin binding properties of the two cell lines and those of control normal pancreatic ductal cells was that soybean agglutinin (SBA) bound to both cell lines, but not to controls. These newly established cell lines should be useful models that will contribute to clarifying the biological and biochemical characteristics of pancreatic cancer.     

A patient with rectal cancer associated with ulcerative colitis in whom endoscopic ultrasonography was useful for diagnosis

Endoscopic ultrasonography (EUS) was helpful for the diagnosis of rectal cancer associated with ulcerative colitis. The patient was a 38-year-old Japanese man with a 19-year history of relapsing-remitting type ulcerative colitis involving the entire colon. Routine colonoscopy revealed multiple polypoid prominences in the upper portion of the rectum. EUS revealed a hypoechoic mass in the submucosa beneath and around the polypoid lesion on the most oral side. Signet ring cells were found in a biopsy specimen from this lesion. Subtotal colectomy was performed. A depressed lesion was observed around the prominence on the most oral side; histologically, this lesion was poorly differentiated mucinous and signet ring cell carcinoma extending into the subserosa. The polypoid lesion on the most anal side was well differentiated adenocarcinoma, which was limited to the mucosa. Our findings suggest that EUS is helpful for detecting invasive cancer associated with ulcerative colitis. Received: April 22, 1998 / Accepted: January 22, 1999     

普通型胃癌伴神经内分泌分化的免疫组织化学观察

目的研究普通型胃腺癌组织学类型、分化程度与神经内分泌（NE）分化的关系.方法随机收集88例手术切除石蜡包埋的胃癌标本,采用Syn、CgA及NSE等3种神经内分泌抗体,用免疫组织化学方法研究其神经内分泌的表达情况.结果在88例普通型胃癌中,38例（43.2%）表达Syn,13例（14%）表达CgA,10例（11%）表达NSE.58例（65.9%）至少有一种NE标记表达,其中18例表达2种标记,仅4例3种标记均表达,3种标记表达彼此相关（P＜0.05）.胃癌中以低分化腺癌、黏液腺癌、印戒细胞癌阳性多见（P＜0.05）.NE阳性与肿瘤大小和浸润深度有关（P＜0.05）,但是NE标志阳性与淋巴转移及临床分期差异无统计学意义（P＞0.05）.结论选择3种NE标记可以检测出胃癌的NE分化,三者联合应用可提高NE分化的诊断率.胃癌的组织类型、分化程度及肿瘤大小和浸润深度与NE分化有关,而NE分化与淋巴结转移及临床分期无关.     

原发性阑尾黏液腺癌一例报告并文献复习

原发性阑尾腺癌可分为黏液腺癌、结肠腺癌类型、杯状细胞癌和印戒细胞癌。原发性阑尾黏液腺癌罕见,病因不明。术前误诊率高。现报道原发性阑尾黏液腺癌一例,并进行文献复习。     

Platelet-derived growth factor-BB (PDGF-BB) regulation of migration and focal adhesion kinase phosphorylation in rabbit aortic vascular smooth muscle cells: roles of phosphatidylinositol 3-kinase and mitogen-activated protein kinases.

OBJECTIVE: Phosphatidylinositol 3'-kinase (PI3-kinase) is implicated in cell migration and focal adhesion kinase (FAK) phosphorylation. In contrast, it has been proposed that mitogen-activated protein (MAP) kinases are essential for proliferation but may be dissociated from chemotactic signalling. We investigated the roles of PI3-kinase and p42/p44 MAP kinases in cell migration and FAK tyrosine phosphorylation induced by platelet-derived growth factor-BB (PDGF-BB) in rabbit aortic vascular smooth muscle cells (VSMCs). The roles of PI3-kinase and MAP kinase pathways in the chemotactic response to insulin-like growth factor-I (IGF-I) were also examined. METHODS: The roles of PI3-kinase and p42/p44 MAP kinases were assessed using the PI3-kinase inhibitors, wortmannin and LY294002, and an inhibitor of MAP kinase kinase, PD98059. PI3-kinase activity was measured by phosphatidylinositol phosphorylation in anti-phosphotyrosine immunoprecipitates and by thin layer chromatography of phosphorylated products. Phosphorylation was assessed by immunoprecipitation with anti-phosphotyrosine antibodies and Western blotting with FAK-specific antibody. Migration was evaluated in a chemotaxis chamber using polycarbonate filters with an 8-mm pore size. RESULTS: Neither wortmannin nor LY294002 significantly reduced PDGF-BB stimulation of FAK tyrosine phosphorylation, chemotaxis or immunofluorescent staining of focal adhesions in VSMCs. PD98059, a specific inhibitor of MAP kinase activation, did not inhibit FAK tyrosine phosphorylation but markedly inhibited the migratory response of VSMCs to PDGF-BB. IGF-I also stimulated migration of VSMCs, and, relative to the effect of PDGF-BB, induced smaller increases in PI3-kinase and MAP kinase activities. Both wortmannin and PD98059 partially inhibited the migratory response to IGF-I. CONCLUSIONS: PDGF-BB stimulation of both FAK tyrosine phosphorylation and migration in VSMCs are not dependent on activation of PI3-kinase. While PDGF-BB stimulation of FAK tyrosine phosphorylation is not dependent on p42/p44 MAP kinase activation, PDGF-BB and IGF-I both stimulate p42/p44 MAP kinase activity and the chemotactic response to these factors is partially dependent on MAP kinase activation.     

胃腺癌组织中分泌血管活性肠肽的肿瘤细胞研究

目的　研究胃腺癌中是否存在分泌血管活性肠肽 (VIP)的肿瘤细胞 ,探讨VIP在胃腺癌发生发展中的作用。方法　 2 0 0 1- 12～ 2 0 0 2 - 0 5通过免疫组化的方法 ,检测华中科技大学同济医院附属协和医院 15例正常胃窦黏膜、2 0例胃腺癌组织中VIP蛋白的表达情况 ,观察样本中VIP阳性反应的细胞和神经纤维。结果　 8例 (8/2 0 )胃腺癌组织中发现VIP阳性细胞 ,其中高分化 2例 (2 / 5 )、中分化 2例 (2 / 7) ,低分化 4例 (4/ 8)。阳性细胞的检出率与胃腺癌的恶性程度无相关性 (P >0. 0 5 )。阳性细胞形态不规则 ,多数细胞核膜及核着色 ,少数胞浆着色 ,核大而不规则。 6例局限分布于肿瘤组织中 ,2例低分化胃腺癌阳性细胞散在分布于整个肿瘤组织中。胃腺癌组织中未见阳性神经纤维 ,正常胃黏膜可见阳性神经纤维 ,但未发现阳性细胞。结论　 4 0 %胃腺癌组织中含有分泌VIP的肿瘤细胞 ,VIP可能对胃腺癌的发生有重要的影响。     

Pseudomesotheliomatous presentation of primary signet ring cell carcinoma of lung

Signet ring cell carcinoma is a unique mucin secreting adenocarcinoma. It generally arises from stomach, colon, rectum or breast and rarely from lung. Pleural membrane involvement is common in lung cancer manifesting as pleural effusion. Rarely, it may encase the whole lung without effusion mimicking mesothelioma and is termed as "pseudomesothelioma". A 35-year-old male presented with a pleural mass encasing the whole of the right lung without any pleural effusion and investigations revealed it to be primary signet ring cell adenocarcinoma of the lung.     

Accuracy of staging laparoscopy in detecting peritoneal dissemination in patients with gastroesophageal adenocarcinoma

Despite staging laparoscopy (SL) with peritoneal lavage is recommended in US Guidelines in patients with potentially resectable gastroesophageal adenocarcinoma, this procedure is not systematically proposed in French Guidelines. Therefore, we decided to analyze the results of systematic SL in patients considered for preoperative chemotherapy. From 2005 to 2011, 116 consecutive patients with distal esophagus, esogastric junction, and gastric adenocarcinoma ≥T3 or N+ without detectable metastatic dissemination by computed tomography (CT) scan imaging underwent SL before neoadjuvant chemotherapy. Positive and negative SLs were compared according to tumor characteristics. SL was positive in 15 cases (12.9%) including 14 with peritoneal seeding (localized in five, diffuse in nine). SL was positive in 7 (24.1%) of 29 patients with poorly differentiated tumor, in 9 (32.1%) of 28 patients with signet ring cells, in 7 (50%) of 14 patients with gastric linitis tumor, and in 15 (16.3%) of 92 patients with T3 or T4 tumor. All the lesions of distal esophagus extending to the cardia had a negative SL. Among the 14 patients with peritoneal carcinomatosis at SL, nine (65%) had signs of peritoneal seeding on initial CT scan. One (0.8%) patient had a small bowel perforation closed laparoscopically. If systematic SL before preoperative chemotherapy does not seem justified because of its low accuracy, it should be performed in patients with poorly differentiated tumor, signet ring cell, and gastric linitis plastica components on biopsy and when CT scan is suggestive of T4 tumor, ascites, or peritoneal nodule.     

Insulin like growth factor-I induces limited association of phosphatidylinositol 3-kinase to its receptor.

Stimulation by insulin-like growth factor-I (IGF-I) of LISN C4 cells, a mouse fibroblast cell line that overexpresses human IGF-I receptors, led to an increase in the amount of a phosphatidylinositol kinase that could be immunoprecipitated by anti-IGF-I receptor or anti-phosphotyrosine antibodies. The identity of the lipid produced in phosphatidylinositol kinase assays of anti-IGF-I receptor or anti-phosphotyrosine immunoprecipitates indicated that IGF-I selectively increased the amount of immunoprecipitated phosphatidylinositol 3-kinase activity. The amount of immunoprecipitated phosphatidylinositol 3-kinase activity that was increased by IGF-I followed a time course that paralleled the stimulation of IGF-I receptor beta-subunit autophosphorylation. The amount of phosphatidylinositol 3-kinase activity detected in anti-IGF-I receptor immunoprecipitates represented only 2% of that which was immunoprecipitated by anti-phosphotyrosine antibody. Furthermore, phosphatidylinositol 3-kinase activity which was recovered with anti-phosphotyrosine antibody was present in both cytosol and particulate cell fractions at approximately similar levels. Taken together, these results suggest that the stimulation of the IGF-I receptor tyrosine kinase leads to an increase in the amount of phosphatidyl inositol 3-kinase activity immunoprecipitated by antiphosphotyrosine and anti-IGF-I receptor antibodies and to a limited association with the IGF-I receptor itself, even though these cells express very high levels of IGF-I receptors. That the majority of phosphatidylinositol 3-kinase activity does not tightly associate with the IGF-I receptor after IGF-I stimulation suggests that it may be associated with other tyrosine phosphorylated proteins. Alternatively, the kinase itself may become phosphorylated on tyrosine and dissociate from the IGF-I receptor. In this manner, an increase of phosphatidylinositol 3-kinase activity by IGF-I deviates from the activation of phosphatidylinositol 3-kinase by platelet-derived growth factor receptor in that a tight association with the receptor is not produced after stimulation.