MYL9：肌球蛋白“細胞動力馬達”家族一員，癌細胞遷移動力靶點？
日期：2023-07-12 17:15:38
MYL9作為肌球蛋白的調(diào)節(jié)性輕鏈（myosin light chain，MLC），是激活肌球蛋白運動活性的關鍵環(huán)節(jié)，為細胞運動提供動力。然而，細胞遷移是造成惡性腫瘤轉(zhuǎn)移的關鍵。多項研究表明，MYL9為癌細胞遷移提供動力，參與腫瘤的發(fā)生、發(fā)展。CD69被認為是淋巴細胞的早期激活標志物，最新研究闡明了一種新機制，MYL9可以作為CD69的配體，參與T細胞募集到炎癥性肺部 [1]。
此外，MYL9-CD69系統(tǒng)可誘導腫瘤微環(huán)境中的效應T細胞衰竭，并削弱抗腫瘤免疫反應。通過阻斷MYL9和CD69之間的相互作用，有利于保持較高的抗腫瘤免疫反應 [2]。因此，MYL9作為肌球蛋白“細胞動力馬達”家族一員，可能是癌癥免疫治療的下一個新藥物靶點！
1. 什么是肌球蛋白？
肌球蛋白是一類高度保守的蛋白，是細胞骨架的重要組成部分，也是基于肌動蛋白依賴性的分子馬達。肌球蛋白約占人體總蛋白的15%~25%，主要存在平滑肌中，其家族比較大，目前已發(fā)現(xiàn)人40個肌球蛋白基因，分別代表12類的超大家族（I-XII）。肌球蛋白的分子結構包括重鏈（myosin heavy chain，MHC）和輕鏈（myosin light chain，MLC），輕鏈又分為基礎性MLC（MLC I）和調(diào)節(jié)性MLC（MLC II）。肌球蛋白是一種多功能蛋白質(zhì)，在細胞的變形、黏附、運動及細胞的遷移方面有巨大的作用，被稱為“細胞動力的馬達”（圖1） [3-6]。
圖1. 肌球蛋白超家族 [3]
2. 什么是MYL9？
肌球蛋白監(jiān)管輕鏈MYL9（myosin regulatory light chain 9，又稱MLC2, MRLC1或MLC-2C）是組成肌球蛋白的調(diào)節(jié)性輕鏈。人MYL9基因位于染色體20q11.23上，包含8621個堿基，8個內(nèi)含子和17個外顯子。它編碼的20KD肌球蛋白監(jiān)管輕鏈，是肌球蛋白的重要組成部分。肌球蛋白按區(qū)域分為頭部、頸部和尾部。頭部是球形，含有ATP結合和肌動蛋白結合部位，用于催化ATP的水解釋放化學能量，并與肌動蛋白結合。頸部有兩條調(diào)節(jié)性輕鏈纏繞成α螺旋狀，可結合肌球蛋白輕鏈和鈣調(diào)素。尾部是卷曲的螺旋結構，含有羥基 （圖2）[7]。
MYL9在正常組織及腫瘤組織中均廣泛表達，如肌肉組織、內(nèi)臟組織、肺癌、前列腺癌等。迄今為止，已有大量研究表明，MYL9作為肌球蛋白的關鍵成員，通過多種調(diào)節(jié)因子參與生物體內(nèi)諸多的功能，如肌肉運動，細胞遷移，細胞內(nèi)吞，有絲分裂和信號轉(zhuǎn)導等，尤其在腫瘤細胞的遷移和增殖中發(fā)揮著重要的作用 [8-11]。
圖2. MYL9是肌球蛋白“細胞動力馬達”關鍵成員 [7]
3. MYL9相關的信號通路
MYL9主要通過兩大系統(tǒng)起到調(diào)控的作用：1）Rho肌酶（rho-kinase, ROCK）系統(tǒng)；2）肌球蛋白輕鏈肌酶（myosin light chain kinase, MLCK）系統(tǒng)。除了這兩個系統(tǒng)之外，還涉及鈣調(diào)蛋白依賴的蛋白激酶II、ILK、PKA、ZIPK、PKC以及肌球蛋白輕鏈磷酸酶MLCP抑制分子CP17等相關重要分子 [12-14]。
如圖3所示，MLCK和ROCK系統(tǒng)激活，并與鈣離子Ca2+結合，增加細胞內(nèi)鈣離子Ca2+濃度，又可以激活肌球蛋白輕鏈肌酶活性和MYL9的磷酸化。具體而言，ROCK是肌球蛋白輕鏈的最直接底物之一，其介導MYL9基因的磷酸化及去磷酸化作用。此外，ROCK可促進細胞內(nèi)Ca2+濃度的增加，通過激活Ca2+／鈣調(diào)蛋白依賴的MLCK，在MLCK的作用下引起MYL9的磷酸化 [12]。
MYL9的磷酸化增強肌球蛋白和肌動蛋白之間的相互作用，以及肌球蛋白輕鏈頭部ATP酶的活性，從而促進細胞骨架的重構，并增加細胞的增殖、分化、粘附和遷移的能力。RhoA抑制因子能有效的直接抑制其下游的效應蛋白Rock，從而對MYL9的表達和磷酸化作用起抑制作用，進而抑制腫瘤細胞肌動蛋白形成等生物學行為，同時對腫瘤的侵襲、轉(zhuǎn)移和生長也起抑制作用 [12]。
圖3. MYL9主要通過MLCK和ROCK兩大系統(tǒng)起到調(diào)控的作用 [12]
4. MYL9在腫瘤等疾病中的作用
許多研究表明，MYL9通過磷酸化和去磷酸化調(diào)節(jié)ATP酶活性以及肌球蛋白的收縮，從而控制細胞的運動、黏附和變形等功能。惡性腫瘤的特點之一是浸潤性生長和遠處轉(zhuǎn)移，這表明與細胞運動相關的分子MYL9異常表達可能影響腫瘤的發(fā)展。許多研究已經(jīng)報道了MYL9參與腫瘤發(fā)病機制，不僅能抑制腫瘤，同時也能促進腫瘤生長 [15-17]。
4.1 MYL9和腫瘤
4.1.1 MYL9促進腫瘤
MYL9在多種腫瘤中呈現(xiàn)增加的表達和磷酸化水平。在乳腺癌和肝癌中，MYL9主要通過促進腫瘤細胞運動來促使腫瘤發(fā)生侵襲 [18-19]。此外，在膠質(zhì)母細胞瘤中，MYL9的表達量和磷酸化水平也有所增加。高水平的MYL9表達與膠質(zhì)母細胞瘤患者預后較差以及復發(fā)性膠質(zhì)母細胞瘤患者中MYL9表達增加相關聯(lián) [8]。另外，胰腺導管腺癌和卵巢上皮性腫瘤中也觀察到MYL9的增加表達。臨床數(shù)據(jù)分析提示MYL9可作為胰腺導管腺癌和卵巢上皮性腫瘤的獨立預后因素 [14, 20]。
同樣地，食管鱗狀細胞癌細胞系中MYL9呈顯著上調(diào)，并且與腫瘤細胞中MYL9表達高的患者總生存期和無復發(fā)生存期較差相關 [21]。此外，高表達MYL9促進骨肉瘤的進展 [22]。綜上所述，這些研究結果表明MYL9可能通過促進腫瘤細胞運動影響腫瘤的生長和侵襲轉(zhuǎn)移，并且可能成為多種腫瘤的預后標志物和治療靶點。
4.1.2 MYL9抑制腫瘤
但與之相反的是，基于微陣列和蛋白質(zhì)組學分析，發(fā)現(xiàn)MYL9蛋白在前列腺組織中表達下降，與年齡、病理分期、轉(zhuǎn)移和PSA水平等相關 [23]。類似地，在膀胱癌和胃癌中也觀察到MYL9表達下調(diào) [24-25]。然而，進一步的細胞實驗證明，MYL9缺乏減少了胃癌細胞的增殖并增強了細胞凋亡 [15]。在人類結直腸癌中，MYL9的表達和磷酸化水平降低 [26]。細胞實驗證實，通過上調(diào)MYL9，可以抑制腫瘤細胞的增殖、侵襲和遷移，并促進結腸癌干細胞的凋亡 [27-28]。
生物信息學分析發(fā)現(xiàn)，低MYL9表達可能與非小細胞肺癌的發(fā)展和轉(zhuǎn)移有關 [29-30]。在乳腺癌中，MYL9的上調(diào)顯著降低了癌細胞的運動能力 [15]。然而，一些文獻提出MYL9在分子水平上的表達增加了乳腺癌細胞的遷移 [15, 31]。根據(jù)目前的文獻，MYL9在惡性腫瘤中的作用存在爭議?？傮w而言，MYH9在腫瘤中的作用復雜多樣，可能成為治療靶點和預后評估的重要指標。
4.2 MYL9和其它疾病
MYL9不僅與腫瘤相關，還在心血管、炎癥和神經(jīng)系統(tǒng)等疾病中發(fā)揮作用 [32-35]。動脈粥樣硬化模型顯示，隨著斑塊增加，MYL9表達顯著下調(diào)。MYL9受到血管緊張素II（Angiotensin II/AGT）和細胞因子PDGF-BB的刺激下調(diào)。血管緊張素II和PDGF-BB是重要的細胞因子，在血管損傷過程中促進平滑肌細胞增殖和遷移。因此，MYL9可能在動脈粥樣硬化的發(fā)展中起重要作用 [36-37]。
陸續(xù)的報道表明MYL9蛋白是CD69分子的新配基，MYL9-CD69系統(tǒng)參與調(diào)節(jié)免疫應答 [2, 38-41]。阻斷MYL9-CD69之間的互動可改善實驗鼠的過敏性呼吸道炎癥，如哮喘 [2]；在炎癥時，血管受損并導致血小板活化，進而產(chǎn)生MYL9網(wǎng)絡結構和各種凝血因子，接著MYL9能夠與CD69陽性的特異性T細胞結合，促使免疫細胞聚集到炎癥部位，并產(chǎn)生效應細胞因子和趨化因子，從而有效激活免疫反應（圖4） [41]。
圖4. MYL9-CD69系統(tǒng)參與調(diào)節(jié)免疫應答 [42]
5. MYL9的臨床研究前景
MYL9在肺癌、乳腺癌、前列腺癌、胃癌等多種不同類型的惡性腫瘤中均有異常表達，并且往往與不良預后密切相關，其表達的臨床意義根據(jù)癌組織的不同而不同。更值得關注的是，MYL9可能作為CD69新配體，兩者的相互作用促進CTL的滯留，使其受到腫瘤抗原的慢性刺激而導致T細胞衰竭。在腫瘤微環(huán)境中，抗原特異性細胞毒性T細胞（cytotoxic lymphocytes，CTL）是機體抗腫瘤免疫的重要防線。這意味著抗MYL9/CD69可能是癌癥免疫療法的理想治療靶點。
目前，國內(nèi)外針對MYL9抗癌的臨床實踐經(jīng)驗尚淺，但其作為各類腫瘤治療的靶標的可能性已得到了越來越多的證據(jù)支持。因此，MYL9作為分子標志物和潛在的靶標，在惡性腫瘤的早期診斷、預后預測以及靶向治療中將具有極大的臨床應用價值。
為鼎力協(xié)助科研和藥企人員針對MYL9在腫瘤等疾病中的臨床應用研究，CUSABIO推出MYL9活性蛋白（Code: CSB-YP015318HU）產(chǎn)品，助力您在MYL9機制方面的研究或其潛在臨床價值的探索。（點擊查看MYL9系列產(chǎn)品： MYL9蛋白； MYL9抗體）
Recombinant Human Myosin regulatory light polypeptide 9(MYL9) (Active) (Code: CSB-YP015318HU)
The Greater than 95% as determined by SDS-PAGE. (Tris-Glycine gel) Discontinuous SDS-PAGE (reduced) with 5% enrichment gel and 15% separation gel.
Immobilized Human MYL9 at 2μg/mL can bind Anti-MYL9 recombinant antibody (CSB-RA015318MA1HU), the EC50 is 4.628-6.430 ng/mL.
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