SummaryOnly graminaceous monocots possess the Strategy II iron (Fe)-uptake system in which Fe is absorbed by roots as an Fe 3þ -phytosiderophore. In spite of being a Strategy II plant, however, rice (Oryza sativa) contains the previously identified Fe 2þ transporter OsIRT1. In this study, we isolated the OsIRT2 gene from rice, which is highly homologous to OsIRT1. Real-time PCR analysis revealed that OsIRT1 and OsIRT2 are expressed predominantly in roots, and these transporters are induced by low-Fe conditions. When expressed in yeast (Saccharomyces cerevisiae) cells, OsIRT2 cDNA reversed the growth defects of a yeast Fe-uptake mutant. This was similar to the effect of OsIRT1 cDNA. OsIRT1-and OsIRT2-green fluorescent protein fusion proteins localized to the plasma membrane when transiently expressed in onion (Allium cepa L.) epidermal cells.OsIRT1 promoter-GUS analysis revealed that OsIRT1 is expressed in the epidermis and exodermis of the elongating zone and in the inner layer of the cortex of the mature zone of Fe-deficient roots. OsIRT1 expression was also detected in the ccompanion cells. Analysis using the positron-emitting tracer imaging system showed that rice plants are able to take up both an Fe 3þ -phytosiderophore and Fe 2þ . This result indicates that, in addition to absorbing an Fe 3þ -phytosiderophore, rice possesses a novel Fe-uptake system that directly absorbs the Fe 2þ , a strategy that is advantageous for growth in submerged conditions.

The programmed cell death 4 gene (PDCD4), a newly identified transformation suppressor, was analysed in lung tumour cell lines and primary lung carcinomas. Reduced PDCD4 mRNA expression was observed in two immortalized lung cell lines and 18 cancer cell lines by northern blot analysis. In the survey of primary lung tumours, PDCD4 cDNA was poorly represented in 47 lung tumours compared with normal lung tissue by cDNA microarray analysis and this poor representation was significantly associated with high-grade (G3) adenocarcinomas (p = 0.012). Immunohistochemical analysis of 124 primary carcinomas comprising all subtypes demonstrated that PDCD4 protein expression was widely lost in tumour samples (83%) and was negatively related to poor prognosis (p = 0.013). The loss of PDCD4 expression correlated with higher grade and disease stage (p = 0.045 and 0.034, respectively), but not tumour size and nodal status. Similarly to the cDNA data, lack of PDCD4 expression was significantly linked to tumour grade in adenocarcinoma (n = 59, p = 0.048), while in squamous cell carcinoma (n = 58), no relationship between PDCD4 expression and clinicopathological parameters was established. These data suggest that the loss of PDCD4 expression is a prognostic factor in lung cancer and may correlate with tumour progression.

An mRNA differential display comparison of mouse JB6 promotionsensitive (P؉) and -resistant (P؊) cells identified a novel gene product that inhibits neoplastic transformation. The JB6 P؉ and P؊ cells are genetic variants that differ in their transformation response to tumor promoters; P؉ cells form anchorage-independent colonies that are tumorigenic, and P؊ cells do not. A differentially displayed fragment, A7-1, was preferentially expressed in P؊ cells at levels >10-fold those in P؉ cells, making its mRNA a candidate inhibitor of neoplastic transformation. An A7-1 cDNA was isolated that was identical to murine Pdcd4 gene cDNAs, also known as MA-3 or TIS, and analogous to human H731 and 197͞15a. Until now, the function of the Pdcd4 protein has been unknown. Paralleling the mRNA levels, Pdcd4 protein levels were greater in P؊ than in P؉ cells. Pdcd4 mRNA was also expressed at greater levels in the less progressed keratinocytes of another mouse skin neoplastic progression series. To test the hypothesis that Pdcd4 inhibits tumor promoter-induced transformation, stable cell lines expressing antisense Pdcd4 were generated from parental P؊ cells. The reduction of Pdcd4 proteins in antisense lines was accompanied by acquisition of a transformation-sensitive (P؉) phenotype. The antisense-transfected cells were reverted to their initial P؊ phenotype by overexpression of a Pdcd4 sense fragment. These observations demonstrate that the Pdcd4 protein inhibits neoplastic transformation.

The programmed cell death 4 (PDCD4) gene was originally identified as a tumor-related gene in humans and acts as a tumor-suppressor in mouse epidermal carcinoma cells. However, its function and regulatory mechanisms of expression in human cancer remain to be elucidated. We therefore investigated the expression of PDCD4 in human hepatocellular carcinoma (HCC) and the role of PDCD4 in human HCC cells. Downregulation of PDCD4 protein was observed in all HCC tissues tested compared with corresponding noncancerous liver, as revealed by Western blotting or immunohistochemical staining. Human HCC cell line, Huh7, transfected with PDCD4 cDNA showed nuclear fragmentation and DNA laddering characteristic of apoptotic cells associated with mitochondrial changes and caspase activation. Transforming growth factor-b1 (TGF-b1) treatment of Huh7 cells resulted in increased PDCD4 expression and occurrence of apoptosis, also concomitant with mitochondrial events and caspase activation. Transfection of Smad7, a known antagonist to TGF-b1 signaling, protected cells from TGF-b1-mediated apoptosis and suppressed TGF-b1-induced PDCD4 expression. Moreover, antisense PDCD4 transfectants were resistant to apoptosis induced by TGF-b1. In conclusion, these data suggest that PDCD4 is a proapoptotic molecule involved in TGF-b1-induced apoptosis in human HCC cells, and a possible tumor suppressor in hepatocarcinogenesis.