Buckling of actin-coated membranes under application of a local force.

The mechanical properties of composite membranes obtained by self-assembly of actin filaments with giant fluid vesicles are studied by micromanipulation with optical tweezers. These complexes exhibit typical mechanical features of a solid shell, including a finite in-plane shear elastic modulus ( approximately 10(-6) N/m). A buckling instability is observed when a localized force of the order of 0.5 pN is applied perpendicular to the membrane plane. Although predicted for polymerized vesicles, this is the first evidence of such an instability.

Viscoelastic properties of actin-coated membranes.

In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study the interaction between these basic components, we designed an in vitro self-assembled network of actin filaments attached to the outer surface of giant unilamellar vesicles. Optical tweezers and single-particle tracking experiments are used to study the rich dynamics of these actin-coated membranes (ACM). We show that microrheology studies can be carried out on such an individual microscopic object. The principle of the experiment consists in measuring the thermally excited position fluctuations of a probe bead attached biochemically to the membrane. We propose a model that relates the power spectrum of these thermal fluctuations to the viscoelastic properties of the membrane. The presence of the actin network modifies strongly the membrane dynamics with respect to a fluid, lipid bilayer one. It induces first a finite (omega=0) two-dimensional (2D) shear modulus G(0)(2D) approximately 0.5 to 5 microN/m in the membrane plane. Moreover, the frequency dependence at high frequency of the shear modulus [G(')(2D)(f ) approximately f(0.85+/-0.07)] and of the bending modulus (kappa(ACM)(f) approximately f(0.55+/-0.21)) demonstrate the viscoelastic behavior of the composite membrane. These results are consistent with a common exponent of 0.75 for both moduli as expected from our model and from prior measurements on actin solutions.

Microrheology of biopolymer-membrane complexes.

We create tailored microstructures, consisting of complexes of lipid membranes with self-assembled biopolymer shells, to study the fundamental properties and interactions of these basic components of living cells. We measure the mechanical response of these artificial structures at the micrometer scale, using optical tweezers and single-particle tracking. These systems exhibit rich dynamics that illustrate the viscoelastic character of the quasi-two-dimensional biopolymer network. We present a theoretical model relating the rheological properties of these membranes to the observed dynamics.

Human chromosome 16 suppresses metastasis but not tumorigenesis in rat prostatic tumor cells.

Genomic aberrations at the chromosome 16q arm are one of the most consistent abnormalities observed by loss of heterozygosity and comparative genomic hybridization analyses in human prostate cancer, suggesting that there are tumor suppressor or metastasis suppressor genes encoded by this chromosomal region. To functionally identify such suppressor genes, we have conducted microcell-mediated chromosome transfer to introduce human chromosome 16 into the highly metastatic Dunning rat prostatic cancer cell line, AT6.1. The metastatic ability of the resultant microcell hybrid clones was then tested in a standard spontaneous metastasis assay using SCID mice. When the microcell-mediated chromosome transfer hybrid cells containing whole human chromosome 16 were injected, the number of metastatic lesions in the lung was significantly reduced as much as 99% on average. Therefore, chromosome 16 has a strong activity to suppress the metastatic ability of AT6.1 cells while it did not affect the tumorigenesis and tumor growth rate. A PCR analysis of various microcell hybrid clones with sequence-tagged site markers indicates that the metastasis suppressor activity is located in the q24.2 region of chromosome 16. Our results are consistent with the previous finding that the region of human chromosome 16q has frequent loss of heterozygosity in prostate cancer patients and suggest that there is a metastasis suppressor gene in this region that may play an important role in the progression of prostate cancer.

Cost effectiveness of routine gonadotropin and androgen measurements in hirsute women.

Many physicians routinely measure the gonadotropins PRL, LH, and FSH and the androgens dehydroepiandrosterone (DHEA), androstenedione (ADIONE), and testosterone, as well as testosterone's biologically active fractions in the evaluation of hirsute women. Is this cost effective? To answer this question, 38 consecutive premenopausal hirsute women were evaluated. Two women each had minor elevations in PRL and FSH, and 11 had minor elevations in LH. Three women had minor elevations in the LH/FSH ratio, and only one was above a ratio of 3, believed to be indicative of polycystic ovarian syndrome. Because these gonadotropin elevations did not correlate with the androgens measured and were of no value in the diagnosis or management of these women, they were not believed to be cost effective. Their routine measurements should be abandoned.

Corticosteroids and adrenal suppression. Characterising and avoiding the problem.

Glucocorticoids are used for a variety of illnesses. One of their major complications is suppression of the hypothalamic-pituitary-adrenal axis, rendering a patient unable to respond to stress. The risk of this suppression may be minimised by the use of short-acting glucocorticoid preparations, administration of the entire daily dose in the early morning, use of topical and intra-articular preparations where appropriate, and the use of alternate-day therapy where appropriate. Most importantly, glucocorticoids should be used cautiously when indicated, and the duration of therapy limited as much as possible.

Side-effects of spironolactone therapy in the hirsute woman.

Spironolactone, an aldosterone antagonist with antiandrogenic activities, is often used to treat hirsute women. Several investigators have reported beneficial effects of such treatment, but the dosages used and side-effects encountered differ in their reports. To clarify this issue, 26 consecutive premenopausal women with idiopathic hirsutism were prospectively evaluated during spironolactone treatment. Sixteen women initially received 100 mg spironolactone twice daily on days 4-21 of their menstrual cycles. In 11 women (68%), the dosage had to be decreased or the medication discontinued due to side-effects. The major side-effect, metrorrhagia with 14-day cycles, occurred in 9 women (56%). This side-effect, while not dangerous, was intolerable to these women. In one woman, spironolactone was discontinued because of urticaria and in another because of scalp hair loss. Ten women initially received 50 mg spironolactone twice daily on days 4-21 of their menstrual cycles. Two developed metrorrhagia, but no other side-effects were noted. Because of the incidence of metrorrhagia at higher dosages, we recommend that spironolactone be administered cyclically at a starting dosage of 50 mg twice daily on days 4-21 of the menstrual cycle. Alternatively, one may consider adding cyclical estrogen/progesterone therapy to continuous spironolactone therapy.