Relationship of the meniscofemoral ligaments of the knee to lateral meniscus tears: magnetic resonance imaging evaluation

This study sought to determine if the presence or absence of meniscofemoral ligaments exerts an influence on the prevalence of tears of the lateral meniscus. We reviewed the sagittal and coronal magnetic resonance images of 173 knees for lateral meniscus tears and the presence of the meniscofemoral ligaments. One or both meniscofemoral ligaments were present in 142 of 173 knees (82%). Fifty-four knees had lateral meniscus tears, 27 of which involved the posterior horn. Thirty-three percent of knees with meniscofemoral ligaments had a lateral meniscus tear, and 23% of knees without meniscofemoral ligaments had a lateral meniscus tear (no significant difference). We found no association between the presence of the meniscofemoral ligaments and tears of the lateral meniscus. Our study questions the importance of preserving or reconstructing these ligaments in instances of meniscal transplantation.     

Functional domains of the alpha1 catalytic subunit of the AMP-activated protein kinase

The AMP-activated protein kinase is a heterotrimeric enzyme, important in cellular adaptation to the stress of nutrient starvation, hypoxia, increased ATP utilization, or heat shock. This mammalian enzyme is composed of a catalytic alpha subunit and noncatalytic beta and gamma subunits and is a member of a larger protein kinase family that includes the SNF1 kinase of Saccharomyces cerevisiae. In the present study, we have identified by truncation and site-directed mutagenesis several functional domains of the alpha1 catalytic subunit, which modulate its activity, subunit association, and protein turnover. C-terminal truncation of the 548-amino acid (aa) wild-type alpha1 protein to aa 312 or 392 abolishes the binding of the beta/gamma subunits and dramatically increases protein expression. The full-length wild-type alpha1 subunit is only minimally active in the absence of co-expressed beta/gamma, and alpha1(1-392) likewise has little activity. Further truncation to aa 312, however, is associated with a large increase in enzyme specific activity, thus revealing an autoinhibitory sequence between aa 313 and 392. alpha-1(1-312) still requires the phosphorylation of the activation loop Thr-172 for enzyme activity, yet is now independent of the allosteric activator, AMP. The increased levels of protein expression on transient transfection of either truncated alpha subunit cDNA are because of a decrease in enzyme turnover by pulse-chase analysis. Taken together, these data indicate that the alpha1 subunit of AMP-activated protein kinase contains several features that determine enzyme activity and stability. A constitutively active form of the kinase that does not require participation by the noncatalytic subunits provides a unique reagent for exploring the functions of AMP-activated protein kinase.     

The role of integrins and extracellular matrix in anchorage-independent growth of a mammary carcinoma cell line

Anchorage-independent growth is a property of malignant cells. Extracellular matrix proteins are present in tumor spheroids but their function is not clearly defined. In this paper we show that a murine mammary carcinoma cell line, SP1, which expresses the fibronectin receptor alpha 5 beta 1 requires fibronectin for anchorage-independent growth in soft agar. Growth factors (hepatocyte growth factor and transforming growth factor-beta) also promote SP1 colony growth. In contrast, collagen types I and IV have an inhibitory effect on SP1 colony growth. A clone isolated from SP1 cells which expresses the collagen/laminin receptor alpha 2 beta 1 as well as the fibronectin receptor alpha 5 beta 1, demonstrates increased colony formation in the presence of fibronectin and collagen. These data suggest a role for both the alpha 5 beta 1 and alpha 2 beta 1 integrin receptors in the regulation of anchorage-independent growth of mammary carcinoma cells.     

Which types of hospital mergers save consumers money?

This study analyzes the changes in costs and prices from 1986 to 1994 for more than 3,500 U.S. short-term general hospitals, including 122 horizontal mergers. These mergers were generally financially beneficial to consumers, providing average price reductions of approximately 7 percent. Merger-related price reductions were considerably less in market areas with higher market concentration levels. Merger-related price reductions in areas with higher penetration by health maintenance organizations (HMOs) were approximately twice those in areas with lower HMO penetration. Merger-related price reductions were greater for low-occupancy hospitals, nonteaching hospitals, nonsystem hospitals, similar-size hospitals, and hospitals with greater premerger service duplication.