Albumin Suppresses Human Hepatocellular Carcinoma Proliferation and the Cell Cycle

Abstract

Many investigations have revealed that a low recurrence rate of hepatocellular carcinoma (HCC) is associated with high serum albumin levels in patients; therefore, high levels of serum albumin are a major indicator of a favorable prognosis. However, the mechanism inhibiting the proliferation of HCC has not yet been elucidated, so we investigated the effect of serum albumin on HCC cell proliferation. Hep3B was cultured in MEM with no serum or containing 5 g/dL human albumin. As control samples, Prionex was added to generate the same osmotic pressure as albumin. After 24-h incubation, the expressions of α-fetoprotein (AFP), p53, p21, and p57 were evaluated with real-time PCR using total RNA extracted from the liver. Protein expressions and the phosphorylation of Rb (retinoblastoma) were determined by Western blot analysis using total protein extracted from the liver. For flow cytometric analysis of the cell cycle, FACS analysis was performed. The percentages of cell cycle distribution were evaluated by PI staining, and all samples were analyzed employing FACScalibur (BD) with appropriate software (ModFit LT; BD). The cell proliferation assay was performed by counting cells with using a Scepter handy automated cell counter (Millipore). The mRNA levels of AFP relative to Alb(−): Alb(−), Alb(+), and Prionex, were 1, 0.7 ± 0.2 (p < 0.001 for Alb(−)), and 1 ± 0.3, respectively. The mRNA levels of p21 were 1, 1.58 ± 0.4 (p = 0.007 for Alb(−) and p = 0.004 for Prionex), and 0.8 ± 0.2, respectively. The mRNA levels of p57 were 1, 4.4 ± 1.4 (p = 0.002 for Alb(−) and Prionex), and 1.0 ± 0.1, respectively. The protein expression levels of Rb were similar in all culture media. The phosphorylation of P807/811 and P780 of Rb protein was reduced in Alb(+). More cells in the G0/G1 phase and fewer cells in S and G2/M phases were obtained in Alb(+) than in Alb(−) (G0/G1: 60.9%, 67.7%, 61.5%; G2/M: 16.5%, 13.1%, 15.6%; S: 22.6%, 19.2%, 23.0%, Alb(−), Alb(+), Prionex, respectively). The same results were obtained in HepG2. Cell proliferation was inhibited in 5 g/dL albumin medium in both HepG2 cells and Hep3B cells in 24 h culture by counting cell numbers. The presence of albumin in serum reduces the phosphorylation of Rb proteins and enhances the expression of p21 and p57, following an increase in the G0/G1 cell population, and suppresses cell proliferation. These results suggest that albumin itself suppresses the proliferation of hepatocellular carcinoma.

An HCC Aggressiveness Index and Blood GTP, Bilirubin and Platelet Levels

“…A second possibility is that the liver parameters actually have HCC-modifying functions. Thus, albumin has been shown to subdue HCC cell growth [33]; HCC-specific GGT isoforms are membrane glycoproteins that catalyze the first enzymatic step in the metabolism of glutathione and is important in maintaining intracellular cysteine and glutathione levels [34][35][36], ALKP might modulate cancer drug resistance [37] as might bilirubin [38,39]. Furthermore, platelet factors have HCC-stimulatory properties [24].…”

Silencing of survivin by YM155 induces apoptosis and growth arrest in hepatocellular carcinoma cells

“…Rb is another generally acknowledged cell-cycle regulator, downstream of survivin (20,26,27). Rb protein primarily presents as a hypophosphorylated form within quiescent cells, whereas its phosphorylation promotes cell proliferation and tumorigenesis (14,15,20,(26)(27)(28). In the present study, p-Rb was used as an indicator to assess the proliferation profile of HCC cells.…”

“…It is well established that Rb protein functions as a cell-cycle suppressor, and its functional loss through protein phosphorylation has been implicated to the tumorigenesis of various types of neoplasm (14,15). Therefore, the phosphorylation level of Rb protein in HCC was investigated.…”

Acylglycerol kinase promotes the proliferation and cell cycle progression of oral squamous cell carcinoma

“…The transition to S phase is induced by the activation of the cyclin D/CDK complex, which phosphorylates Rb, a well-characterized regulator of cell proliferation (9,24,25). In addition, this complex activates cyclin E/CDK 2 by sequestering the CDK inhibitor p21 (7,26). p21 inhibits cell cycle progression at checkpoint G 1 , where it results in sustained G 1 blockade (26,27).…”

“…In addition, this complex activates cyclin E/CDK 2 by sequestering the CDK inhibitor p21 (7,26). p21 inhibits cell cycle progression at checkpoint G 1 , where it results in sustained G 1 blockade (26,27). To elucidate the potential underlying mechanisms of the effects of AGK, the expression levels of numerous cell cycle-associated molecules, including cyclin D1 and p21, and cell cycle distribution were investigated.…”