Unbalanced growth in mouse cells with amplified dhfr genes

When grown in the absence of methotrexate, cells carrying unstably amplified dihydrofolate reductase (dhfr) genes have a growth disadvantage that is a function of their level of gene amplification. Although this growth disadvantage is thought to drive the loss of unstably amplified dhfr genes in the absence of methotrexate, its mechanism is not understood. The present studies of murine cell lines with different levels of dhfr gene amplification demonstrate that such cells experience increased unbalanced growth (excess RNA and protein content relative to DNA content) with increased levels of dhfr gene amplification. Stathmokinetic analysis of a cell line with unstably amplified dhfr genes showed that the unbalanced growth was associated with a very low rate of G1/S transit, which suggests that amplified DNA sequences may activate a cell cycle checkpoint at the G1/S boundary. Hydroxyurea, which is known to induce rapid elimination of amplified genes at sub-cytotoxic concentrations, also inhibits the cell cycle at the G1/S transition and causes unbalanced growth. Earlier work has shown that hydroxyurea selectively targets those cells within the heterogeneous drug resistant cell populations which have the highest amplified gene dosage. The finding that unstable gene amplification and hydroxyurea have similar effects on the cell suggests that hydroxyurea may achieve this selective targeting by pushing those cells with the highest levels of gene amplification over a critical stress threshold to cause growth arrest or cell death.

CHIME-Net, the Connecticut Health Information Network: a pilot study

CHIME-Net is a state-wide community health information network project which uses a frame-relay approach to interfacility and internet connectivity. This is a collaborative effort among competitive institutions, which embraces technologies new to the health care industry. The experiences of implementation of the CHIME-Net pilot project are presented as a first milestone for the state-wide effort.

A frame-relay approach for a state-wide health information network

An approach for a frame-relay implementation is described which is intended to establish connectivity between the health care providers in the state of Connecticut with a gateway to the internet. While other health care networking efforts have based the interconnectivity efforts on direct connections to the internet for each institution, our design takes a more cost effective approach by establishing a private health care network with a single entry point to the internet. This will not only provide the advantages of internet connections to all participating providers, but it will also isolate intrastate patient care traffic from the internet, reserving internet traffic for those information needs not available within the statewide network. In addition to the network solution, an extensive user support infrastructure is also presented.