Yu Yinhua, Luo Robert, Lu Zhen, Wei Feng Wei, Badgwell Donna, Issa Jean-Pierre, Rosen Daniel G, Liu Jinsong, Bast Robert C
The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Methods Enzymol. 2006;407:455-68. doi: 10.1016/S0076-6879(05)07037-0.
ARHI is a maternally imprinted tumor suppressor gene that is downregulated in 60% of ovarian and breast cancers. Loss of ARHI expression is associated with tumor progression in breast cancer and decreased disease-free survival in ovarian cancer. ARHI encodes a 26-kDa protein with 55-62% homology to Ras and Rap. In contrast to Ras, ARHI inhibits growth, motility, and invasion. ARHI contains a unique 34 amino-acid extension at its N-terminus and differs from Ras in residues critical for GTPase activity and for its putative effector function. Deletion of ARHI's unique N-terminal extension markedly reduces its inhibitory effect on cell growth. The gene maps to chromosome 1p31 at a site of LOH in 40% of ovarian and breast cancers. Mutations have not been detected, but the remaining allele is silenced by methylation in approximately 10-15 % of cases. In the remaining cancers, ARHI is downregulated by transcriptional mechanisms that involve E2F1 and E2F4, as well as by the loss of RNA binding proteins that decrease the half-life of ARHI mRNA. Transgenic expression of human ARHI in mice produces small stature, induces ovarian atrophy, and prevents postpartum milk production. Reexpression of ARHI in cancer cells inhibits signaling through Ras/Map and PI3 kinase, upregulates P21(WAF1/CIP1), downregulates cyclin D1, induces JNK, and inhibits signaling through STAT3. Marked overexpression of ARHI with a dual adenoviral vector induces caspase-independent, calpain-dependent apoptosis. When ARHI is expressed from a doxycycline-inducible promoter at more physiological levels, autophagy is induced, rather than apoptosis. Growth of ovarian and breast cancer xenografts is reversibly suppressed by ARHI, but expression of the NTD mutant produced only a limited inhibitory effect on growth of xenografts.
ARHI是一种母系印记的肿瘤抑制基因，在60%的卵巢癌和乳腺癌中表达下调。ARHI表达缺失与乳腺癌的肿瘤进展以及卵巢癌无病生存期缩短有关。ARHI编码一种26 kDa的蛋白质，与Ras和Rap有55 - 62%的同源性。与Ras不同，ARHI抑制生长、运动和侵袭。ARHI在其N端含有一个独特的34个氨基酸的延伸序列，在对GTP酶活性及其假定效应功能至关重要的残基上与Ras不同。删除ARHI独特的N端延伸序列会显著降低其对细胞生长的抑制作用。该基因定位于1p31染色体上，在40%的卵巢癌和乳腺癌中该位点存在杂合性缺失。尚未检测到突变，但在大约10 - 15%的病例中，剩余的等位基因通过甲基化而沉默。在其余的癌症中，ARHI通过涉及E2F1和E2F4的转录机制以及通过降低ARHI mRNA半衰期的RNA结合蛋白的缺失而下调。人ARHI在小鼠中的转基因表达导致身材矮小，诱导卵巢萎缩，并阻止产后泌乳。ARHI在癌细胞中的重新表达抑制通过Ras/Map和PI3激酶的信号传导，上调P21(WAF1/CIP1)，下调细胞周期蛋白D1，诱导JNK，并抑制通过STAT3的信号传导。用双腺病毒载体显著过表达ARHI可诱导不依赖半胱天冬酶、依赖钙蛋白酶的凋亡。当ARHI从强力霉素诱导型启动子以更生理水平表达时，会诱导自噬而非凋亡。ARHI可可逆地抑制卵巢癌和乳腺癌异种移植物的生长，但NTD突变体的表达对异种移植物的生长仅产生有限的抑制作用。
