Fig 1.
The levels and subcellular distribution of GOLPH3 are different in different human breast cell lines.
(A) Cell homogenates (H) from the indicated cell lines were used to prepare cytosolic (C) and membrane (M) fractions. Equivalent amounts of each fraction (10 μg of proteins) were subjected to SDS-PAGE and immunoblotting using antibodies to the proteins indicated on the right. The position of molecular mass markers is indicated on the left. (B) Densitometric quantification of the immunoblot signal of the levels of GOLPH3 in the cell homogenates as shown in (A). (C) Densitometric quantification of the immunoblot signal of the levels of GOLPH3 in cytosolic (C) and membrane (M) fractions as shown in (A). Bar represents the mean ± standard deviation of the amount of immunoblot signal normalized with the signal for β-actin, and also for the total amount of protein in each fraction (for more details see S1 Table). *** P < 0.001; ns, not statistically significant.
Fig 2.
GOLPH3 from MCF7 cells is more tightly bound to membranes than in MCF 10A or MDA-MB-231 cells.
(A-C) Samples of a membrane fraction (70 μg of proteins) from MCF 10A (A), MCF7 (B), and MDA-MB-231 (C) cells were incubated on ice for 1 hour with either 10 mM Tris HCl pH 7.4 (Control), 1 M KCl in 10 mM Tris HCl pH 7.4 (KCl) or 0.2 M Na2CO3 pH 11.3 (Na2CO3). After centrifugation, pelleted membranes (P) and extracted proteins in the supernatant (S) were processed by SDS-PAGE and immunoblotting using antibodies to the proteins indicated on the right. Syn16, Syntaxin 16. The position of molecular mass markers is indicated on the left. (D-F) Densitometric quantification of the immunoblot signal of the levels of GOLPH3 in pellets (P) and supernatants (S) as shown in A-C of membranes incubated in control conditions (D), in 1 M KCl (E), or in 0.2 M Na2CO3 (F). Bar represents the mean ± standard deviation of the amount of immunoblot signal. * P < 0.05; ** P < 0.01; *** P < 0.001.
Fig 3.
Cytosolic GOLPH3 behaves as a monomer in MCF 10A, MCF7, and MDA-MB-231 cells.
Samples of a cytosolic fraction from the indicated cell lines were analyzed by gel filtration on a Superose 6 column. Arrows indicate the elution position of molecular size markers. Stokes radii (Rs) are indicated in Angstroms (Å). As a reference, the molecular mass (M) of molecular size markers is also indicated. Fractions were subjected to SDS-PAGE and immunobloting with antibodies to the proteins indicated on the right. The position of molecular mass markers is indicated on the left.
Fig 4.
The sensitivity of GOLPH3 to BFA is different in different human breast cell lines.
NRK (A and B), MCF 10A (C and D), MDA-MB-231 (E and F), and MCF7 (G and H) cells were left untreated (Control) or treated with 5 μg/ml BFA for 60 min (BFA). Cells were fixed, permeabilized, and immunolabeled with rabbit polyclonal antibody to GOLPH3, mouse monoclonal antibody to GM130, and either sheep antibody to TGN38 (A and B) or sheep antibody to TGN46 (C to H). Secondary antibodies were Alexa-594-conjugated donkey anti-rabbit IgG (red channel), Alexa-488-conjugated donkey anti-mouse IgG (green channel), and Alexa-647-conjugated donkey anti-sheep IgG (blue channel). Stained cells were examined by fluorescence microscopy. Merging red, green, and blue channels generated the fourth image on each row; yellow indicates overlapping localization of the red and green channels, cyan indicates overlapping localization of the green and blue channels, magenta indicates overlapping localization of the red and blue channels, and white indicates overlapping localization of all three channels. Insets show 1.7x magnifications. Bar, 10 μm.
Fig 5.
The dynamic behavior of GFP-GOLPH3 is different in different human breast cell lines.
(A-C) MCF 10A (A), MDA-MB-231 (B), and MCF7 (C) cells transiently expressing GFP-GOLPH3 were held in a microscope stage at 37°C and examined by fluorescence microscopy. The time after initiation of imaging is shown in the bottom right corner of each panel in minutes:seconds. Images are representative of 15–20 videos of up to 200 seconds of recording. In B, filled arrows indicate a vesicular structure moving from the Golgi to the periphery of the cell. In C, filled arrows indicate a vesicular structure moving from the periphery of the cell to the Golgi area, and filled arrowheads indicate a tubular structure elongating from the Golgi. Empty arrows and empty arrowheads indicate the initial position of mobile structures. Bars, 5 μm. (D-F) The number of tubule-vesicular structures moving centrifugally (D), the number of tubular structures elongating from the Golgi (E), or the number of tubule-vesicular structures moving centripetally (F), were quantified from videos corresponding to 180 seconds of imaging. Bar represents the mean + standard deviation of the observed profiles (n = 15). * P < 0.05; *** P < 0.001.
Fig 6.
The Golgi-associated fluorescence after photobleaching of GFP-GOLPH3 recovers partially in MCF7 cells.
(A-C) MCF 10A (A), MDA-MB-231 (B), and MCF7 (C) cells transiently expressing GFP-GOLPH3 were held in a microscope stage at 37°C. The area indicated by a white dotted-line rectangle in each set of images was bleached with a 488-nm laser set to 100% power. The fluorescence recovery after photobleaching (FRAP) was tracked by laser confocal microscopy with the 488-nm laser set to 2% power. Images were acquired before bleaching (Pre-bleaching), immediately after bleaching (Bleaching), and during the recovery of the fluorescence (Recovery) at approximately every 0.4-sec. Images of a representative experiment performed on each cell line are shown in each set of panels. Two images of the recovery of fluorescence are depicted with the time indicated in parenthesis in seconds. Bar, 10 μm. (D) Plot of the FRAP analysis of GFP-GOLPH3 in MCF 10A (black circles; n = 10), MDA-MB-231 (white circles; n = 10), and MCF7 (white squares; n = 10) cells. P, pre-bleaching; B; bleaching. For simplicity, error bars are not depicted. *** P < 0.001; ns, not statistically significant. The halftime (t1/2) of maximal fluorescence recovery is indicated on the right in seconds (s).
Fig 7.
The cytosolic and membrane pools of GOLPH3 are differentially modified in different human breast cell lines.
Samples (30 μg of proteins) of rat liver cytosol (Cyt), rat liver Golgi membranes, and of cytosolic (Cyt) and membrane (Memb) fractions from the cell lines indicated at the right were analyzed by two-dimensional gel electrophoresis (2-D GE) and immunoblotting using antibody to GOLPH3. Samples of rat liver Golgi membranes, and of the cytosolic and membrane fractions of each cell line, were dephosphorylated with calf intestine alkaline phosphatase (CIAP) before processing for 2-D GE. The position of molecular mass markers is indicated on the left. The position of isoelectric point (pI) markers is indicated at the bottom. Red asterisks indicate the position of additional, less abundant, but distinct spots in the samples of MCF7 cells that have slightly slower electrophoretic mobility. Numbers indicate different acidic forms identified in immunoblot films subjected to different exposure times.
Fig 8.
The cytosol of different human breast cell lines affects differently the avidity of GOLPH3 for phosphatidylinositol 4-phosphate.
(A) Membranes with the spotted phospholipids indicated on the left were incubated with untreated, recombinant GOLPH3 (GOLPH3) or with recombinant GOLPH3 in the presence of cytosolic proteins from the cell lines indicated on the top. Bound recombinant GOLPH3 was detected by immunoblotting with antibody to GOLPH3. LysoPtdA, lysophosphatidic acid; LysoPtdCho, lysophosphatidylcholine; PtdIns, phosphatidylinositol; PtdIns(3)P, phosphatidylinositol 3-phosphate; PtdIns(4)P, phosphatidylinositol 4-phosphate; PtdIns(5)P, phosphatidylinositol 5-phosphate; PtdEth, phosphatidylethanolamine; PtdCho, phosphatidylcholine; S1P, sphingosine 1-phosphate; PtdIns(3,4)P2, phosphatidylinositol 3,4-bisphosphate; PtdIns(3,5)P2, phosphatidylinositol 3,5-bisphosphate; PtdIns(4,5)P2, phosphatidylinositol 4,5-bisphosphate; PtdIns(3,4,5)P3, phosphatidylinositol 3,4,5-trisphosphate; PtdA, phosphatidic acid; PtdSer, phosphatidylserine; Blank, no lipid. (B) Densitometric quantification of the immunoblot signal of the levels of untreated, recombinant GOLPH3 bound to different phospholipids as shown in (A). (C) Densitometric quantification of the immunoblot signal of the levels of recombinant GOLPH3 bound to phosphatidylinositol 4-phosphate after incubation with cytosolic proteins of the indicated cell lines as shown in (A). * P < 0.05; *** P < 0.001.