Mechanical convergence in mixed populations of mammalian epithelial cells

Tissues consist of cells with different molecular and/or mechanical properties. Measuring the forces and stresses in mixed-cell populations is essential for understanding the mechanisms by which tissue development, homeostasis, and disease emerge from the cooperation of distinct cell types. However, many previous studies have primarily focused their mechanical measurements on dissociated cells or aggregates of a single-cell type, leaving the mechanics of mixed-cell populations largely unexplored. In the present study, we aimed to elucidate the influence of interactions between different cell types on cell mechanics by conducting in situ mechanical measurements on a monolayer of mammalian epithelial cells. Our findings revealed that while individual cell types displayed varying magnitudes of traction and intercellular stress before mixing, these mechanical values shifted in the mixed monolayer, becoming nearly indistinguishable between the cell types. Moreover, by analyzing a mixed-phase model of active tissues, we identified physical conditions under which such mechanical convergence is induced. Overall, the present study underscores the importance of in situ mechanical measurements in mixed-cell populations to deepen our understanding of the mechanics of multicellular systems.

Accumulation of annexin A2 and S100A10 prevents apoptosis of apically delaminated, transformed epithelial cells

In various epithelial tissues, the epithelial monolayer acts as a barrier. To fulfill its function, the structural integrity of the epithelium is tightly controlled. When normal epithelial cells detach from the basal substratum and delaminate into the apical lumen, the apically extruded cells undergo apoptosis, which is termed anoikis. In contrast, transformed cells often become resistant to anoikis and able to survive and grow in the apical luminal space, leading to the formation of multilayered structures, which can be observed at the early stage of carcinogenesis. However, the underlying molecular mechanisms still remain elusive. In this study, we first demonstrate that S100A10 and ANXA2 (Annexin A2) accumulate in apically extruded, transformed cells in both various cell culture systems and murine epithelial tissues in vivo. ANXA2 acts upstream of S100A10 accumulation. Knockdown of ANXA2 promotes apoptosis of apically extruded RasV12-transformed cells and suppresses the formation of multilayered epithelia. In addition, the intracellular reactive oxygen species (ROS) are elevated in apically extruded RasV12 cells. Treatment with ROS scavenger Trolox reduces the occurrence of apoptosis of apically extruded ANXA2-knockdown RasV12 cells and restores the formation of multilayered epithelia. Furthermore, ROS-mediated p38MAPK activation is observed in apically delaminated RasV12 cells, and ANXA2 knockdown further enhances the p38MAPK activity. Moreover, the p38MAPK inhibitor promotes the formation of multilayered epithelia of ANXA2-knockdown RasV12 cells. These results indicate that accumulated ANXA2 diminishes the ROS-mediated p38MAPK activation in apically extruded transformed cells, thereby blocking the induction of apoptosis. Hence, ANXA2 can be a potential therapeutic target to prevent multilayered, precancerous lesions.

FBP17-mediated finger-like membrane protrusions in cell competition between normal and RasV12-transformed cells

At the initial stage of carcinogenesis, cell competition often occurs between newly emerging transformed cells and the neighboring normal cells, leading to the elimination of transformed cells from the epithelial layer. For instance, when RasV12-transformed cells are surrounded by normal cells, RasV12 cells are apically extruded from the epithelium. However, the underlying mechanisms of this tumor-suppressive process still remain enigmatic. We first show by electron microscopic analysis that characteristic finger-like membrane protrusions are projected from both normal and RasV12 cells at their interface. In addition, FBP17, a member of the F-BAR proteins, accumulates in RasV12 cells, as well as surrounding normal cells, which plays a positive role in the formation of finger-like protrusions and apical elimination of RasV12 cells. Furthermore, cdc42 acts upstream of these processes. These results suggest that the cdc42/FBP17 pathway is a crucial trigger of cell competition, inducing “protrusion to protrusion response” between normal and RasV12-transformed cells.

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EM analysis shows finger-like membrane protrusions between normal and RasV12 cells

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Cdc42/FBP17 regulate the formation of the finger-like membrane protrusions

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Cdc42/FBP17-mediated finger-like protrusions promote elimination of RasV12 cells

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‘Protrusion to protrusion response’ triggers cell competition

The CD44/COL17A1 pathway promotes the formation of multilayered, transformed epithelia

At the early stage of cancer development, oncogenic mutations often cause multilayered epithelial structures. However, the underlying molecular mechanism still remains enigmatic. By performing a series of screenings targeting plasma membrane proteins, we have found that collagen XVII (COL17A1) and CD44 accumulate in RasV12-, Src-, or ErbB2-transformed epithelial cells. In addition, the expression of COL17A1 and CD44 is also regulated by cell density and upon apical cell extrusion. We further demonstrate that the expression of COL17A1 and CD44 is profoundly upregulated at the upper layers of multilayered, transformed epithelia in vitro and in vivo. The accumulated COL17A1 and CD44 suppress mitochondrial membrane potential and reactive oxygen species (ROS) production. The diminished intracellular ROS level then promotes resistance against ferroptosis-mediated cell death upon cell extrusion, thereby positively regulating the formation of multilayered structures. To further understand the functional role of COL17A1, we performed comprehensive metabolome analysis and compared intracellular metabolites between RasV12 and COL17A1-knockout RasV12 cells. The data imply that COL17A1 regulates the metabolic pathway from the GABA shunt to mitochondrial complex I through succinate, thereby suppressing the ROS production. Moreover, we demonstrate that CD44 regulates membrane accumulation of COL17A1 in multilayered structures. These results suggest that CD44 and COL17A1 are crucial regulators for the clonal expansion of transformed cells within multilayered epithelia, thus being potential targets for early diagnosis and preventive treatment for precancerous lesions.

The COX-2/PGE2 pathway suppresses apical elimination of RasV12-transformed cells from epithelia

At the initial stage of carcinogenesis, when RasV12-transformed cells are surrounded by normal epithelial cells, RasV12 cells are apically extruded from epithelia through cell competition with the surrounding normal cells. In this study, we demonstrate that expression of cyclooxygenase (COX)-2 is upregulated in normal cells surrounding RasV12-transformed cells. Addition of COX inhibitor or COX-2-knockout promotes apical extrusion of RasV12 cells. Furthermore, production of Prostaglandin (PG) E2, a downstream prostanoid of COX-2, is elevated in normal cells surrounding RasV12 cells, and addition of PGE2 suppresses apical extrusion of RasV12 cells. In a cell competition mouse model, expression of COX-2 is elevated in pancreatic epithelia harbouring RasV12-exressing cells, and the COX inhibitor ibuprofen promotes apical extrusion of RasV12 cells. Moreover, caerulein-induced chronic inflammation substantially suppresses apical elimination of RasV12 cells. These results indicate that intrinsically or extrinsically mediated inflammation can promote tumour initiation by diminishing cell competition between normal and transformed cells.

Underuse of primary Mycobacterium avium complex and Pneumocystis carinii prophylaxis in the United States

BACKGROUND

Little is known about the rates of Mycobacterium avium complex (MAC) and Pneumocystis carinii (PCP) prophylaxis adherence to guidelines and how they have changed after introduction of effective antiretroviral therapy.

OBJECTIVE

To determine rates of primary prophylaxis for MAC and PCP and to evaluate the influence of sociodemographic characteristics, region, and provider experience.

DESIGN

National probability sample cohort of HIV patients in care.

SETTING

One hundred sixty HIV health care providers.

PATIENTS

A total of 2864 patients interviewed in 1996 to 1997 (68% response) and 2267 follow-up interviews, representing 65% of surviving sampled patients (median follow-up, 15.1 months).

MEASUREMENTS

Use of prophylactic drugs, most recent CD4 count, sociodemographics, and regional and total HIV patients/providers.

RESULTS

Of patients eligible for primary MAC prophylaxis (most recent CD4 count <50/mm(3) ), 41% at baseline and 40% at follow-up patients were treated. Of patients eligible for primary PCP prophylaxis (i.e., those with CD4 counts <200/mm(3) ), 64% and 72% were treated, respectively. MAC prophylaxis at baseline was less likely in African American (adjusted odds ratio [OR], 35; 95% confidence interval [CI], 0.20-0.59), Hispanic (OR, 27; 95% CI, 0.08-0.94) and less-educated (OR, 0.61; 95% CI, 0.36-1.0) patients and more likely in U. S. geographic regions in the Pacific West (OR, 4.9; 95% CI, 1.0-23) and Midwest (OR, 6.4; 95% CI, 1.2-33) and in practices with more HIV patients.

CONCLUSIONS

Most eligible patients did not receive MAC prophylaxis; PCP prophylaxis rates were better but still suboptimal. Our results support outreach efforts to African Americans, Hispanics, the less educated, and those in the northeastern United States and in practices with fewer HIV patients.

National estimates of HIV-related symptom prevalence from the HIV Cost and Services Utilization Study

OBJECTIVES

The objectives of this study were (1) to estimate the prevalence, bothersomeness, and variation of HIV-related symptoms in a nationally representative sample of HIV-infected adults receiving medical care and (2) to evaluate new aggregate measures of symptom frequency and bothersomeness.

METHODS

Beginning in January 1996, 76% of a multistage national probability sample of 4,042 HIV-infected adults receiving medical care were interviewed. Participants endorsed the presence and degree of bothersomeness of 14 HIV-related symptoms during the preceding 6 months. Sex-standardized symptom number and bothersomeness indices were constructed. After sampling weights were incorporated, symptom distributions were compared according to selected characteristics by analysis of variance and multiple linear regression modeling.

RESULTS

Prevalence of specific symptoms in the reference population was as follows: fever/night sweats, 51.1%; diarrhea, 51%; nausea/anorexia, 49.8%; dysesthesias, 48.9%; severe headache, 39.3%; weight loss, 37.1%; vaginal symptoms, 35.6% of women; sinus symptoms, 34.8%; eye trouble, 32.4%; cough/dyspnea, 30.4%; thrush, 27.3%; rash, 24.3%; oral pain, 24.1%; and Kaposi's sarcoma, 4%. Aggregate measures were reliable (Cronbach's alpha > or =0.75) and demonstrated construct validity when compared with other measures of disease severity. After adjustment for CD4 count, both symptom number and bothersomeness varied significantly (P <0.05) by teaching status of care setting, exposure/risk group, educational achievement, sex, annual income, employment, and insurance category. However, the magnitude of variation was small. Symptoms were greatest in women and injection drug users, as well as in persons with lower educational levels, lower income, and Medicare enrollment or those who were followed up at teaching hospitals.

CONCLUSIONS

The prevalence and bothersomeness of HIV-related symptoms are substantial and vary by setting of care and patient characteristics.

The impact of competing subsistence needs and barriers on access to medical care for persons with human immunodeficiency virus receiving care in the United States

OBJECTIVES

To examine whether competing subsistence needs and other barriers are associated with poorer access to medical care among persons infected with human immunodeficiency virus (HIV), using self-reported data.

DESIGN

Survey of a nationally representative sample of 2,864 adults receiving HIV care.

MAIN INDEPENDENT VARIABLES

Going without care because of needing the money for food, clothing, or housing; postponing care because of not having transportation; not being able to get out of work; and being too sick.

MAIN OUTCOME MEASURES

Having fewer than three physician visits in the previous 6 months, visiting an emergency room without being hospitalized; never receiving antiretroviral agents, no prophylaxis for Pneumocystis carinii pneumonia in the previous 6 months for persons at risk, and low overall reported access on a six-item scale.

RESULTS

More than one third of persons (representing >83,000 persons nationally) went without or postponed care for one of the four reasons we studied. In multiple logistic regression analysis, having any one or more of the four competing needs independent variables was associated with significantly greater odds of visiting an emergency room without hospitalization, never receiving antiretroviral agents, and having low overall reported access.

CONCLUSIONS

Competing subsistence needs and other barriers are prevalent among persons receiving care for HIV in the United States, and they act as potent constraints to the receipt of needed medical care. For persons infected with HIV to benefit more fully from recent advances in medical therapy, policy makers may need to address nonmedical needs such as food, clothing, and housing as well as transportation, home care, and employment support.