Production of mouse mammary tumor virus upon transfection of a recombinant proviral DNA into cultured cells

We have investigated the intracellular proteins synthesized in rat XC and feline kidney cells transfected with endogenous mouse mammary tumor virus (MMTV) proviral DNA. The endogenous provirus GR40, associated with the Mtv-8 locus, directs the synthesis of gag proteins indistinguishable from those found in MMTV-infected cells. The env precursor Pr73env and the mature gp52 proteins could not be detected in these cells. Instead an env-related protein of 68K is synthesized. In contrast to this endogenous provirus, a cloned exogenous proviral variant directs the synthesis of apparently normal env proteins upon transfection into the same cell lines. These results suggest that the env gene of the endogenous MMTV provirus GR40 is defective. The exogenous proviral variant is not expected to synthesize virus particles since it carries a rearrangement in the gag gene. In order to obtain an MMTV provirus capable of correctly expressing both gag and env functions, we have constructed a hybrid endogenous-exogenous provirus containing the 5' long terminal repeat (LTR)-gag of GR40 and the pol-env-3' LTR of the exogenous provirus. Upon transfection into feline kidney cells, this hybrid provirus directed the synthesis of apparently authentic gag and env proteins. Further, virus particles can be detected in the culture medium of the transfected cells by electron microscopy. Viral proteins obtained from viral particles banded in a sucrose gradient were detected by immunoprecipitation.     

喹胺酸和LICAM(C)对大鼠体内238Pu和241Am的促排效果比较

喹胺酸(Quinamic acid, QAA, 811)是一种异哇啉类络合剂, 对钍有较好的促排效果。本文主要研究大鼠静脉注入(iv)²³⁸Pu和²⁴¹Am各26kBq/kg后1小时, 经皮下注入(so)不同剂量.(1～30μmol/kg)QAA, 或静脉注入核素后立即灌胃(po)QAA(30μmol/kg)对²³⁸Pu、²⁴¹Am的促排疗效, 并与LICAM(C)相比较。实验观察到QAA对降低骨肝中²³⁸Pu、²⁴¹Am的蓄积量有较好的作用, QAA对²³⁸Pu的促排效果高于对²⁴¹Am.在剂量(1～30μgmol/kg)对肝、肾中²³⁸Pu和骨、肾中²⁴¹Am蓄积量的降低, QAA优于LICAM(C)；灌胃QAA(30μttmol/kg)伍用NaHCO₃(5mmol/kg的)疗效, 对骨、肝中²³⁸Pu蓄积量的降低, QAA和LICAM(C)二间无差异(P>0.05), 但对²³⁸Pu在肾中蓄积量和对²⁴¹Am在骨, 肾中蓄积量的降低, QAA明显优于LICAM(C)。     

The methylation pattern of endogenous mouse mammary tumor virus proviral genes is tissue specific and stably inherited

The methylation pattern of mouse mammary tumor virus (MMTV) proviral genes endogenous to the mouse strains C3H, 020, FM/JmsA, C57BL6, and BALB/c were investigated in various organs and mammary tumor tissue. Digestion of DNA with EcoRI or with EcoRI and HpaII followed by Southern blotting analysis and hybridization to a nick-translated MMTV DNA, allowed the distinction between the fully methylated and hypomethylated gene copies. MMTV proviral gene methylation was found to be organ specific, and the methylation pattern is stably inherited. The same proviral units present in different strains of mice exhibit the same organ-specific methylation patterns. Although proviral genes are normally heavily methylated in all tissues, hypomethylation of endogenous proviral genes was found in organs not known to express MMTV.     

Pre-EMTing metastasis? Recapitulation of morphogenetic processes in cancer

EMT (epithelial–mesenchymal transition) is a morphogenetic process in which cells loose their epithelial characteristics and gain mesenchymal properties during embryogenesis. Similar processes regulated by similar pathways are recapitulated during tumour progression, endowing cells with invasive properties, thereby contributing to the formation of metastases. In this review, we outline key features of EMT and discuss the evidence for its involvement in the dissemination of tumours. Finally we review the recent literature concerning the mechanisms that regulate EMT in the tumour context, with a particular focus on breast cancer.     

Platelet deficiency in <Emphasis Type="Italic">Tpo</Emphasis><Superscript>−/−</Superscript> mice can both promote and suppress the metastasis of experimental breast tumors in an organ-specific manner

Platelets are thought to play an important role in metastasis formation, although the mechanisms involved remain incompletely understood. Here we studied the influence of platelet numbers on organ-specific metastasis to the lungs and lymph nodes using Tpo deficient mice that have low platelet counts. After tail vein injection of 4T1 breast cancer cells, the number of lung metastases was significantly lower in Tpo^?/? mice compared to Tpo^+/+ mice. The same was true for the bone-tropic 4T1.2 derivative. In spontaneous orthotopic metastasis assays, 4T1 and 4T1.2 primary tumor growth was not affected by the genotype of the mice. However, the number of 4T1.2 lung metastases was significantly lower in Tpo^?/? mice compared to Tpo^+/+ mice, whereas the number of 4T1 lung metastases was unaffected. Moreover, in mice bearing 4T1 tumors, lymph node metastases were larger in the Tpo^?/? background, and lymph node metastasis frequency was higher in Tpo^?/? mice bearing 4T1.2 tumors compared to that in wild-type mice. Enhanced lymph node metastasis in Tpo^?/? mice was not associated with changes in peritumoral lymphatic vessel density in the primary tumors. Together, our data indicate that platelets do not affect primary tumor growth in this breast cancer model, but can differentially influence site-specific metastasis to lymph nodes and lungs.