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胃癌至今仍是臺灣地區癌病之主要死亡原因之一，雖然內視鏡檢查的早期發現病灶及外科手術技術的進步已使胃癌病患的存活率較從前增加，迄今胃癌仍高居臺灣地區癌病死亡之第四位；輔助性或姑息性之化學療法、放射線療法及免疫療法對於胃癌提供的療效是相當有限的，因此，對於外科手術無法治癒或無法接受手術的病人，更進一步去瞭解胃癌細胞之生長特性以尋求其他可能的治療方法便顯得相當重要。
目前已知多種生長激素及細胞激素與胃癌病患之預後及腫瘤分期相當有關，其中肝細胞生長因素對於多種細胞具有促進其生長及增加其移動力的特性，所以相當受到重視；體內多種正常甚或腫瘤組織均可分泌此肝細胞生長因素，它可能經由自分泌(autocrine)和旁分泌(paracrine)的機轉來增加正常及腫瘤細胞的增生及移動能力；而由於肝細胞生長因素之接受體已知為一致癌基因一C-met的蛋白質產物，而且此接受體之過度表現亦已被發現與人類胃癌之發生、增生及轉移有關，所以肝細胞生長因素與其接受體之交互作用很可能在胃癌的增生及侵犯轉移上扮演著中樞的角色。本研究發現肝細胞生長因素可刺激人類胃癌細胞之生長，且此細胞增生的程度隨投與之肝細胞生長因素之劑量增加而增加；根據流式細胞分析的檢測，我們發現這種細胞增生的現象乃因細胞週期中G0-G1，期的時間因肝細胞生長因素之投與而縮短所致。細胞膜上肝細胞生長因素接受體c-met的變化亦與細胞週期有關，其濃度自G0-G1，、S至G2-M期逐漸增加；在SC-ML這種胃癌細胞，c-met接受體之濃度會因肝細胞生長因素之刺激而減量，然而這種現象則不見於原先即過度表現c-met接受體於細胞膜之KATO-III細胞。另一方面，肝細胞生長因素方可增加胃癌細胞之移動能力，特別是含高量c-wet接受體之KATO-III細胞，顯示c-met接受體之過度表現可能是胃癌細胞侵犯鄰近組織及遠端轉移的一項指標。
除此之外，肝細胞生長因素可藉由原儲存於細胞胞器內鈣離子之釋放來提升肝細胞胞漿內鈣離子濃度，這種鈣離子的移動咸信是經由肝細胞生長因素與其位於細胞膜上之接受體結合後激發接受體上酥氨酸激酉每(tyrosine kinase)續而引發磷脂酉每C-γ(phospholipaseC-γ)之活化所引起，胞漿中鈣離子的增加則會使細胞膜電位及離子通道產生變化，這些離子變化的情形與肝細胞生長因素引發之肝細胞增生有密切的關係﹔在胃癌細胞中，雖然早已知道肝細胞生長因素可引起細胞的增生與移動而認為此生長因素在胃癌之惡化與轉移中扮演一重要角色，鈣與其他離子訊息在肝細胞生長因素之訊息傳導途徑及其所引發主細胞增生中實際作用機轉為何則仍未明瞭﹔之前有關鈣誘發性鉀離子通道的研究顯示﹕胃癌細胞分泌黏液之作用及變形之MDCK腎細胞移動能力之增加與鈣誘發性鉀離子通道之活性有關，可見此離子通道之活化情況對轉型之癌細胞功能上之變化具相當程度的影響。由於不同的胃癌細胞株對於肝細胞生長因素的刺激有不同的生長反應，而且這些細胞之細胞膜上也確實存在著鈣誘發性鉀離子通道，因此我們進一步利用對這些胃癌細胞的初步瞭解，以細胞膜箝制技術之全細胞記錄(whole cell recordin)模式來探討肝細胞生長因素對於胃癌細胞膜上鈣誘發性鉀離子通道之影響，並且更試圖瞭解此離子通道活性的變化與肝細胞生長因素所引起之細胞增殖是否相關。研究結果顯示，肝細胞生長因素可在SC-M1胃癌細胞中引發一向細胞外流動之鉀離子電流，並使其在將細胞膜箝制在-80mV時之傳導斜率(slopeconductance)由110±15pS/pF增加到207±15pS/pF，這個由肝細胞生長因素所誘發之電流可因在細胞外浸泡液(bathing solution)中加入鉀離子通道阻斷劑tetraethylammonium chloride或在記錄吸管(recording pipette)中加入低鈣溶液阻斷，顯示此一向胞外流動的電流即為鈣誘發性鉀離子電流；除此之外，肝細胞生長因素的刺激更可使此一鈣誘發性鉀離子電流產生波動性的變化。然而在另一含肝細胞生長因素接受體較高之胃癌細胞株灼KATO-III，肝細胞生長因素反而無法誘發此一電流之變化。上述之結果顯示，鈣誘發性鉀離子通道之活性可能與肝細胞生長因素所誘發主胃癌細胞增殖有關。
Gastric cancer appears to be a major problem in Taiwan because of itscommon occurrence and unfavorable prognosis. Surgery remains the principal treatment modality, and adjuvant chemotherapy, radiation therapy and immunotherapy give only limited effects. Therefore, a further understanding of the cell biology of gastric cancer is of paramount importance to improve the treatment result, especially for those patients who are refractory to surgery or unable to undergo surgery.
Several growth factors and cytokines have been proved to be related to gastric cancer growth and some of which associated with tumor''s staging and patient''s prognosis. Among these factors, hepatocyte growth factor (HGF) receives much attention because of its major effects on cell growth and motility. HGF is produced by several tissues, including neoplasms; it can therefore provide a stimulus for increased proliferation and motility of malignant cells by both a paracrine and autocrine mechanism. The receptor for HGF has been identified as the product of oncogene c-met, suggesting that this gene may play an important role in facilitating cellular proliferation and invasion. Overexpression of hepatocyte growth factor receptor (HGFR) has also been linked to tumorigenesis, progression and metastasis in human gastric cancers. In addition HGF stimulation could increase intracellular Ca++ in cancer cells, which may lead to alteration of membrane potential and transmembranous ionic currents. These early ionic events are generally assumed to play important roles in triggering the proliferative response. Whether the HGF-induced responses are correlated with the expressed level of HGF receptors or the changes of ionic currents is not clear.
The present study investigated the effects of HGF on the expression of HGFR, cell proliferation, cell motility and ionic currents of two human gastric adenocarcinoma cell lines. Results showed that the expression of HGFR in both SC-Ml and KATO-III gastric cancer cells was cycle dependent, the level increased from G0-G1 to S phase with the highest level in G2-M phases. HGF treatment induced a dose-dependent growth stimulation and accelerated cell cycle progression in SC-M1 cells.
This effect was in part induced by shortening the duration of G0-G1 phase as examined by flow cytometric analysis of cell cycle. It was also found that HGFR was down-regulated in response to HGF stimulation in SC- M1 gastric cancer cells. On the other hand, it was found that the motility of KATO-III cells was significant higher than that of SC-M1 cells in scatter assay and that HGF enhanced the cell motility in KATO-III but not in SC-M1 cells. Since KATO-III cells have been known to have overexpressed HGFR, it is possible that HGFR status may indicate the invasive and metastatic potential of gastric cancer cells.
In patch clamp study, HGF treatment induced an outward K+ current and increased the slope conductance at -80 mV from 110 ±15 pS/pF to 207 ±15 pS/pF in SC-Ml cells. The HGF-induced K+ current was abolished when tetraethylammonium chloride was added in bathing solution or a low Ca++ solution was included in the recording pipette. Furthermore, HGF (10 ng/ml) induced an oscillatory Ca++-activated K+ current with a lag period of 5 ±3 minutes in SC-Ml cells. In contrast, HGF did not induce mitogenesis, cell cycle progression, down-regulation of HGFR and changes in ionic currents in KATO-III cells, although this cell line expressed a higher level of HGFR than SC-Ml cell did. These findings provide evidence that the activity of Ca++-activated K+ channel may be involved in the HGF-induced cell proliferation in human gastric cancer cells, but it did not correlate with the density of HGFR.
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